CI (macos): Work around conflict between pre-installed and Homebrew Python

[mmuetzel]

Installing packages from Homebrew currently fails with an error like the following:

==> Pouring [email protected]_1.ventura.bottle.tar.gz
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Error: The `brew link` step did not complete successfully
Could not symlink bin/idle3
Target /usr/local/bin/idle3
already exists. You may want to remove it:
  rm '/usr/local/bin/idle3'

To force the link and overwrite all conflicting files:
  brew link --overwrite [email protected]

To list all files that would be deleted:
  brew link --overwrite [email protected] --dry-run

Possible conflicting files are:
/usr/local/bin/idle3 -> /Library/Frameworks/Python.framework/Versions/3.12/bin/idle3
/usr/local/bin/pydoc3 -> /Library/Frameworks/Python.framework/Versions/3.12/bin/pydoc3
/usr/local/bin/python3 -> /Library/Frameworks/Python.framework/Versions/3.12/bin/python3
/usr/local/bin/python3-config -> /Library/Frameworks/Python.framework/Versions/3.12/bin/python3-config
/usr/local/share/man/man1/python3.1 -> /usr/local/Cellar/[email protected]/3.12.7/share/man/man1/python3.1
/usr/local/lib/pkgconfig/python3-embed.pc -> /usr/local/Cellar/[email protected]/3.12.7/lib/pkgconfig/python3-embed.pc
/usr/local/lib/pkgconfig/python3.pc -> /usr/local/Cellar/[email protected]/3.12.7/lib/pkgconfig/python3.pc
/usr/local/Frameworks/Python.framework/Headers -> /usr/local/Cellar/[email protected]/3.12.7/Frameworks/Python.framework/Headers
/usr/local/Frameworks/Python.framework/Python -> /usr/local/Cellar/[email protected]/3.12.7/Frameworks/Python.framework/Python
/usr/local/Frameworks/Python.framework/Resources -> /usr/local/Cellar/[email protected]/3.12.7/Frameworks/Python.framework/Resources
/usr/local/Frameworks/Python.framework/Versions/Current -> /usr/local/Cellar/[email protected]/3.12.7/Frameworks/Python.framework/Versions/Current
==> /usr/local/Cellar/[email protected]/3.13.0_1/bin/python3.13 -Im ensurepip
==> /usr/local/Cellar/[email protected]/3.13.0_1/bin/python3.13 -Im pip install -v --n
==> Summary
🍺  /usr/local/Cellar/[email protected]/3.13.0_1: 3,253 files, 63.2MB

Force overwriting files from the version of Python that is pre-installed on the macOS runner images. They conflict with the files from Homebrew's versions of Python.

That likely means that this part needs to be updated about once every year (if Python keeps its release schedule of one major version release each year and Homebrew keeps up with that).
If someone with better knowledge of Homebrew has a better solution, please let me know. (Ideally one that doesn't require bumping the Python versions every year...)