github actions: upgrade to ubuntu 22.04

[mpollmeier]

ubuntu 18.04 got deprecated https://github.blog/changelog/2022-08-09-github-actions-the-ubuntu-18-04-actions-runner-image-is-being-deprecated-and-will-be-removed-by-12-1-22/

[mpollmeier]

scalafmt ftw :)

I'll better disable it in that file...

[bbrehm]

Yeah, it is far too aggressive. I'd much prefer a setting that is more non-invasive. For example, don't change line-breaks except for the last line, only change whitespace within lines.