fix CI/CD and test badges

[TomLav]

The CI/CD is broken (or was it ever configured correctly?). And the badges show "unknown" status. Can someone help?

[matdevdug]

Be glad to help! Do you want to keep it set up on Travis or can we move it to GitHub Actions?

[TomLav]

That's great if you can move it to GitHub actions. I copied the Travis framework from a colleague or a tutorial at the time, but honestly I do not understand this part.