Prefer Python 3.12 if available

Prefer Python 3.12 if available

This ensures that python3.12 is used testing on older distributions
like EL8 and EL9, where the platform default python3 is older.

python3.11 was explicitly added due to FreeBSD, which doesn't have that
binary symlinked to any other name (like python3). Previously, it worked
only incidentally - when python3 was listed first, it triggered special
meson code for python detection, which is no longer the case when
python3.12 is listed first.