Test `test_try_send_request` is flaky

[Darksonn]

Tokio's CI suite runs all hyper tests on every PR. The test_try_send_request test failed on a PR that only changes documentation, so it is most likely the test that is flaky. The test failure happened on mac os.

failures:

---- conn::test_try_send_request stdout ----
thread 'conn::test_try_send_request' panicked at tests/client.rs:2123:13:
request was returned
stack backtrace:
   0: rust_begin_unwind
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:652:5
   1: core::panicking::panic_fmt
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/panicking.rs:72:14
   2: client::conn::test_try_send_request::{{closure}}::{{closure}}
             at ./tests/client.rs:2123:13
   3: <core::pin::Pin<P> as core::future::future::Future>::poll
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/future/future.rs:123:9
   4: tokio::runtime::task::core::Core<T,S>::poll::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/core.rs:329:17
   5: tokio::loom::std::unsafe_cell::UnsafeCell<T>::with_mut
             at /Users/runner/work/tokio/tokio/tokio/src/loom/std/unsafe_cell.rs:16:9
   6: tokio::runtime::task::core::Core<T,S>::poll
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/core.rs:318:13
   7: tokio::runtime::task::harness::poll_future::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/harness.rs:485:19
   8: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/panic/unwind_safe.rs:272:9
   9: std::panicking::try::do_call
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:559:40
  10: ___rust_try
  11: std::panicking::try
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:523:19
  12: std::panic::catch_unwind
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panic.rs:149:14
  13: tokio::runtime::task::harness::poll_future
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/harness.rs:473:18
  14: tokio::runtime::task::harness::Harness<T,S>::poll_inner
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/harness.rs:208:27
  15: tokio::runtime::task::harness::Harness<T,S>::poll
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/harness.rs:153:15
  16: tokio::runtime::task::raw::poll
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/raw.rs:271:5
  17: tokio::runtime::task::raw::RawTask::poll
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/raw.rs:201:18
  18: tokio::runtime::task::LocalNotified<S>::run
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/task/mod.rs:427:9
  19: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:714:25
  20: tokio::runtime::coop::with_budget
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/coop.rs:107:5
  21: tokio::runtime::coop::budget
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/coop.rs:73:5
  22: tokio::runtime::scheduler::current_thread::Context::run_task::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:348:43
  23: tokio::runtime::scheduler::current_thread::Context::enter
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:412:19
  24: tokio::runtime::scheduler::current_thread::Context::run_task
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:348:23
  25: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:713:35
  26: tokio::runtime::scheduler::current_thread::CoreGuard::enter::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:751:68
  27: tokio::runtime::context::scoped::Scoped<T>::set
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context/scoped.rs:40:9
  28: tokio::runtime::context::set_scheduler::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context.rs:180:26
  29: std::thread::local::LocalKey<T>::try_with
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/thread/local.rs:283:12
  30: std::thread::local::LocalKey<T>::with
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/thread/local.rs:260:9
  31: tokio::runtime::context::set_scheduler
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context.rs:180:9
  32: tokio::runtime::scheduler::current_thread::CoreGuard::enter
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:751:27
  33: tokio::runtime::scheduler::current_thread::CoreGuard::block_on
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:660:19
  34: tokio::runtime::scheduler::current_thread::CurrentThread::block_on::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:180:28
  35: tokio::runtime::context::runtime::enter_runtime
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context/runtime.rs:65:16
  36: tokio::runtime::scheduler::current_thread::CurrentThread::block_on
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:168:9
  37: tokio::runtime::runtime::Runtime::block_on_inner
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/runtime.rs:361:47
  38: tokio::runtime::runtime::Runtime::block_on
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/runtime.rs:335:13
  39: client::conn::test_try_send_request
             at ./tests/client.rs:2061:9
  40: client::conn::test_try_send_request::{{closure}}
             at ./tests/client.rs:2045:37
  41: core::ops::function::FnOnce::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/ops/function.rs:[250](https://github.com/tokio-rs/tokio/actions/runs/10417542180/job/28852042160?pr=6773#step:8:251):5
  42: core::ops::function::FnOnce::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
thread 'conn::test_try_send_request' panicked at tests/client.rs:2126:10:
called `Result::unwrap()` on an `Err` value: JoinError::Panic(Id(96), "request was returned", ...)
stack backtrace:
   0: rust_begin_unwind
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:652:5
   1: core::panicking::panic_fmt
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/panicking.rs:72:14
   2: core::result::unwrap_failed
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/result.rs:1679:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/result.rs:1102:23
   4: client::conn::test_try_send_request::{{closure}}
             at ./tests/client.rs:2061:9
   5: <core::pin::Pin<P> as core::future::future::Future>::poll
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/future/future.rs:123:9
   6: <core::pin::Pin<P> as core::future::future::Future>::poll
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/future/future.rs:123:9
   7: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:673:57
   8: tokio::runtime::coop::with_budget
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/coop.rs:107:5
   9: tokio::runtime::coop::budget
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/coop.rs:73:5
  10: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}
error: test failed, to rerun pass `--test client`
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:673:25
  11: tokio::runtime::scheduler::current_thread::Context::enter
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:412:19
  12: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:672:36
  13: tokio::runtime::scheduler::current_thread::CoreGuard::enter::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:751:68
  14: tokio::runtime::context::scoped::Scoped<T>::set
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context/scoped.rs:40:9
  15: tokio::runtime::context::set_scheduler::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context.rs:180:26
  16: std::thread::local::LocalKey<T>::try_with
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/thread/local.rs:283:12
  17: std::thread::local::LocalKey<T>::with
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/thread/local.rs:[260](https://github.com/tokio-rs/tokio/actions/runs/10417542180/job/28852042160?pr=6773#step:8:261):9
  18: tokio::runtime::context::set_scheduler
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context.rs:180:9
  19: tokio::runtime::scheduler::current_thread::CoreGuard::enter
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:751:27
  20: tokio::runtime::scheduler::current_thread::CoreGuard::block_on
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:660:19
  21: tokio::runtime::scheduler::current_thread::CurrentThread::block_on::{{closure}}
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:180:28
  22: tokio::runtime::context::runtime::enter_runtime
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/context/runtime.rs:65:16
  23: tokio::runtime::scheduler::current_thread::CurrentThread::block_on
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/scheduler/current_thread/mod.rs:168:9
  24: tokio::runtime::runtime::Runtime::block_on_inner
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/runtime.rs:361:47
  25: tokio::runtime::runtime::Runtime::block_on
             at /Users/runner/work/tokio/tokio/tokio/src/runtime/runtime.rs:335:13
  26: client::conn::test_try_send_request
             at ./tests/client.rs:2061:9
  27: client::conn::test_try_send_request::{{closure}}
             at ./tests/client.rs:2045:37
  28: core::ops::function::FnOnce::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/ops/function.rs:250:5
  29: core::ops::function::FnOnce::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


failures:
    conn::test_try_send_request

Tokio runs the hyper test suite on the latest tag, which is v1.4.1 in this case. The PR was based on Tokio master, specifically commit 56f3f40c.