Update FreeBSD CI images

[asomers]

• FreeBSD 12 is EoL. Drop it.
• Use the latest FreeBSD 13 and 14 versions.
• Add FreeBSD 15.0-CURRENT.
• Use the current python version.

Sponsored by: ConnectWise
Signed-off-by: Alan Somers [email protected]

Motivation and Context

Maintenance: test on the latest FreeBSD versions instead of old ones.

Description

Update FreeBSD and Python versions used in CI.

How Has This Been Tested?

None. This change affects CI only.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.