show conformance test status overview

@frankarensmeier had the idea to show the result of the conformance test suite on main in some overview page somewhere. That would be great.

What would need to be done is, I think:

Adjust the github action so that for conformance checks on main only (not PRs) to record the result of the test run (also handling the case if it would fail completely, though we hope that's not possible) and then post it to some service that can record this line of text and display each line as a web page (or even a graph).

I have no idea what kind of services provide this kind of feature but I hope someone else does!