Improve GH Action checks

[tschmidtb51]

Currently, we run the go.yml just on pushs.

@s-l-teichmann Wouldn't it be useful to automatically run it on pull requests as well or was that a specific choice? If we run it on Pull Requests as well, it would make it easier for reviewers to find the obvious mistakes...

I'm happy to implement the change - I just can't remember whether this was an active decision (and if so what the reasons were).

[s-l-teichmann]

@tschmidtb51 Yes, we should do that and there were no active decisions not doing this.
I think this a historical artifact. The amount of external PRs were small and our internal
pushes are triggering the actions.