CI: use gcc-12 for Ubuntu and check use-after-free errors

[lifenjoiner]

Thanks for contributing!

2 facts:

1. -Werror=use-after-free is not that good as expected: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104069
2. The code is too version specific, which will become an issue some day.

Robust code is always preferred.