Instances of type variables bounded by an iterable type support iteration but not unpacking

[tdsmith]

Bug Report

Instances of type variables bounded by an iterable type support iteration but not unpacking.

To Reproduce

from typing import TypeVar

class A:
    pass

ATuple = TypeVar("ATuple", bound=tuple[A, ...])

def f(aa: ATuple) -> None:
    for a in aa:               # this is ok
        print(a)

f((A(),))

def g(aa: ATuple) -> None:
    (a,) = aa                  # "ATuple" object is not iterable
    print(a)

g((A(),))

Bounding the TypeVar by list[A] has the same behaviour as bounding it by tuple[A, ...].

Expected Behavior

No error -- an ATuple should support both iteration and unpacking.

Actual Behavior

f() checks clean.

In g(), unpacking fails with:

error: "ATuple" object is not iterable
error: Cannot determine type of "a"

Your Environment

This reproduces in all versions in the playground.