Rollup merge of #95441 - AlecGoncharow:issue-95204-fix, r=Mark-Simulacrum
Always use system `python3` on MacOS
This PR includes 2 changes:
1. Always use the system Python found at `/usr/bin/python3` on MacOS
2. Removes the hard requirement on having `python` in your system path if you didn't specify alternatives. The proposed change will instead attempt to find and use in order: `python` -> `python3` -> `python2`. This change isn't strictly necessary but without any change to this check, the original issue inspiring this change will still exist.