Test MariaDB 10.5+ and MySQL 8.1+ server versions in Github Actions CI

[pali]

Currently it is not possible to enable MariaDB 10.5+ and MySQL 8.1+ server versions in Github Actions CI because Perl module MySQL::Sandbox reject these new versions during installation phase.

[dveeden]

For DBD::mysql I'm testing with MySQL 8.1+ like this: https://github.com/perl5-dbi/DBD-mysql/blob/master/.github/workflows/ci.yml Feel free to copy this if you want.

I assume you're aware that MySQL::Sandbox got replaced by dbdeployer (both by Giuseppe Maxia) and that the latter seems to become unmaintained as well. See https://datacharmer.github.io/end-of-dbdeployer/ for details.