Replace Travis with GitHub Actions

[ddeboer]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Related tickets
Documentation
License	MIT

What's in this PR?

Replace Travis setup with a GitHub Actions workflow.

Checklist

• Updated CHANGELOG.md to describe BC breaks / deprecations | new feature | bugfix
• Documentation pull request created (if not simply a bugfix)

To Do

• If the PR is not complete but you want to discuss the approach, list what remains to be done here

[dbu]

thanks a lot!

can you rename coverage to "coverage & static" or something like that? and run it on php 8.0? there is a gazillion errors about return types raised by phpstan, i think they would not occur on 8.0.

then we can later separately address the 8.1 deprecations.

[ddeboer]

Done.

[dbu]

thanks a ton!

[dbu]

i thought scrutinizer failed in your fork because it is not the same repository. still fails here. i wonder what we should do. not sure if we need scrutinizer, imho we could also just drop that step.