[CI] Indirect dependency `pyobjc-framework-Metal` 12.0 (via `jaraco.path`) crashes CI for Python 3.9 on macOS

[abravalheri]

Looks like Python 3.9 on macOS is still failing because pyobjc-framework-Metal 12.0 doesn't provide Python 3.9 wheels. So it ends up trying to build from sdist.

pyobjc (transitive dependency of jaraco.path) could be pinned to < 12 on darwin on Python 3.9. Or if it's possible to tell tox to not use sdist (akin to https://pip.pypa.io/en/stable/cli/pip_download/#cmdoption-prefer-binary or https://docs.astral.sh/uv/pip/compatibility/#-only-binary-enforcement )

Originally posted by @Avasam in #5104 (comment)

Ref: ronaldoussoren/pyobjc#661

[Avasam]

For posterity: #5106 (comment)

Assuming PIP_PREFER_BINARY was picked-up correctly, is it possible pip's resolver is not sophisticated enough to walk back to the pyobjc dependency to try a lower bound to avoid pyobjc-*==12 ?