fix(tests): forward Windows home variables through the hermetic test runner

[Sanjays2402]

What does this PR do?

scripts/run_tests.sh runs the suite under env -i so no credential variable can leak into tests. It forwards HOME, which is enough on POSIX, but native Windows CPython resolves Path.home() from USERPROFILE (or HOMEDRIVE + HOMEPATH), and other platform directories come from LOCALAPPDATA/APPDATA. With those stripped, collection can fail on native Windows for any test that touches Path.home().

This forwards those five location variables through the hermetic boundary, and pins PYTHONIOENCODING=utf-8 so child pytest output decodes consistently on CP936/CP932 hosts.

The credential allowlist is unchanged. These are location variables, not secrets, and each one is forwarded only when it is actually set, so a POSIX run produces the exact same environment it did before.

Related Issue

Fixes #70813

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• scripts/run_tests.sh: build a WIN_ENV array from USERPROFILE, HOMEDRIVE, HOMEPATH, LOCALAPPDATA, APPDATA (only when set) and expand it into the exec env -i argument list; add PYTHONIOENCODING=utf-8.
• tests/scripts/test_run_tests_sh_env.py: new guard covering the forwarded variables, the set-only behavior, the UTF-8 pin, and that credential variables are still absent from the allowlist.

How to Test

1. .venv/bin/python -m pytest tests/scripts/test_run_tests_sh_env.py -q → 13 passed.
2. Revert scripts/run_tests.sh and rerun → 8 failed, 5 passed (RED verified on unpatched main; the 5 that still pass are the credential-scrubbing assertions, which must not regress).
3. bash -n scripts/run_tests.sh → clean.
4. On POSIX, USERPROFILE/LOCALAPPDATA/APPDATA are unset, so the env -i line is unchanged.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix
• I've added tests for my changes
• I've tested on my platform: macOS 26.5 (Apple Silicon)

Documentation & Housekeeping

• I've updated relevant documentation — N/A (no user-facing config or docs surface changes)
• I've updated cli-config.yaml.example — N/A
• I've updated CONTRIBUTING.md / AGENTS.md — N/A
• I've considered cross-platform impact — this is the cross-platform fix; POSIX behavior is unchanged because the variables are only forwarded when set

[alt-glitch]

This was generated by AI during triage.

Related: this fixes #70813 and overlaps the native-Windows hermetic-runner approaches in #67387 and #67512; maintainers should select the preferred scope.