Bump minimum PHP version to 8.1 & misc maintenance

[mfn]

Summary

• Bump minimum PHP version to 8.1 & misc maintenance Laravel 10 doesn't support 8.0 anyway and our github actions already reflect that and don't test this version
• Remove phpunit 9 It's not required anymore, Laravel 10+ support phpunit 10+
• gha: remove unused matrix dimension dependency-version (we use stability)
• gha: bump runner os to ubuntu-22.04
• tests: remove outdated version checks

I also took the library and adapted the CHANGELOG slightly, to make it also clear that doctrine/dbal removal actually means Laravel 9 goes out of support, too.

• [x] Misc. change (internal, infrastructure, maintenance, etc.)

Checklist

• [ ] Existing tests have been adapted and/or new tests have been added
• [x] Add a CHANGELOG.md entry
• [ ] Update the README.md
• [ ] Code style has been fixed via composer fix-style

[mfn]

@barryvdh I think things are shaping up nicely, how about a 3.0.0-RC1 preview release?

[barryvdh]

Hmm let's hold off on the RC for just a bit, maybe we want some breaking changes. Was playing around with the phpdoc parser.