Caching for GitHub actions ain't working

[Smephite]

Our Docker GitHub actions won't cache in the step Build and push neither for master branch pushes nor for PRs resulting in build times of >6 Minutes.

Other question: Is this really that bad?

[Triton171]

It's probably not a super high priority issue. Do we have any idea why it happens? If we do and there is a simple fix, it'd be nice to do that, otherwise I think we can postpone it.

[Smephite]

Nope, not the slightest clue.
Didn't really put effort in it tho