docs(release): cover TestPyPI verification and fix stale wheel-download notes

[andygrove]

Which issue does this PR close?

Closes #.

Rationale for this change

Worked through the Python wheel release docs end-to-end on the 53.0.0-rc1-pypitest-3 tag and hit a few rough edges and stale pieces:

• The verification docs ("Verifying Release Candidates") only cover the Rust tarball script. They do not mention that RC verifiers can also install the wheels from TestPyPI to sanity-check the Python artifacts before voting.
• dev/release/download-python-wheels.py aborts in non-interactive shells because the gpg signing step needs a TTY for pinentry. There is no warning in the docs and the failure mode is confusing.
• The expected-files list pins the manylinux_2_17 glibc tag, but the runner image now produces manylinux_2_39 wheels (and that number will keep moving as the GitHub-hosted runner advances).
• The fallback advice says "the build-sdist job currently does not upload its output as a workflow artifact." That is no longer true after ci: produce real aarch64 wheel and upload sdist artifact #1753, which added a dist-sdist artifact. The local-rebuild command in that same block uses maturin build --release --sdist --out dist, which was the broken command (it produces both a wheel and an sdist) fixed in ci: use maturin sdist subcommand to avoid building a wheel #1759.
• The per-platform fallback download still references dist-windows-latest, but ci: pin Windows wheel builder to windows-2022 #1751 renamed it to dist-windows-2022. It also omits the new dist-sdist.
• The TestPyPI smoke test runs python -m venv against whatever python is on PATH. On macOS that is 3.9, and pip then reports a misleading "No matching distribution found" because the wheels are cp310-abi3 (Python ≥ 3.10).

What changes are included in this PR?

dev/release/README.md only:

• New "(Optional) Verify the Python wheels from TestPyPI" subsection under "Verifying Release Candidates".
• Note next to download-python-wheels.py explaining the gpg/non-TTY failure mode and that the traceback is harmless for a TestPyPI-only dry-run.
• Wheel-filename list uses manylinux_* globs instead of the hard-coded manylinux_2_17 tag, with a one-line explanation of why.
• Fallback per-platform gh run download adds dist-sdist and renames dist-windows-latest → dist-windows-2022.
• Drop the stale "build-sdist does not upload" paragraph; replace with a shorter note that local rebuild is rarely needed, using the correct maturin sdist --out dist command.
• Smoke-test venv uses python3.10 and a comment explains why python alone is not enough.

No code, script, or workflow changes.

Are there any user-facing changes?

Documentation only. No runtime or API impact.

[martin-g]

Is it expected/guaranteed that the new version will be at test.pypi.org ?
If the release manager always uploads the wheel to test.pypi.org then this snippet could be added to dev/release/verify-release-candidate.sh and done automatically.