docs: update build badge in READMEi (#5546)
docs: update build badge in READMEi (#5546)

The build badge in the README file was still pointing to an outdated Azure build run from February.
Seems like builds have been migrated to GitHub Actions afterwards.

I used the `tests` workflow, since that seems to be the correct one to replace a *whole* build flow.
monicahq/monica,monicahq/monica