Make sure to use Xcode 16.2 which fixed a clang compiler bug which would
generate incorrect optimized code in the 8g8 feature.

Turn off macos-12 because that has now been removed by GitHub Actions.
We will need to find an alternative way to build official legacy binary
releases.

Also, update Perl version to 5.34 as macOS-15 doesn't come with 5.30
anymore. Perl 5.34 has been installed on macOS 13 and above. Should not
be a huge deal as Perl isn't commonly used for plugins.