[drive-by CI improvement suggestion] Implement a unified gate check for branch protection

[webknjaz]

I have a thing (https://github.com/marketplace/actions/alls-green#why — a shameless plug; you might've seen it integrated in CPython, pip, cryptography, etc.) that allows consolidating results of CI matrixes into a single gate.

The reason I'm bringing this up is that I noticed that only a portion of jobs are marked as required in PRs so it is likely that updating branch protection after updating the CI job definitions slipped off the radar.

This could be a good first issue for an external contributor, requiring just a little GHA experience.

[davisagli]

Thanks @webknjaz. Updating the branch protection rules requires admin permissions on the repository, so I think @sethmlarson has to do it.

[webknjaz]

The workflow/job definition can be implemented separately. But the final bit would require an admin, yes.

[davisagli]

@webknjaz Ah, I misunderstood -- you're not merely proposing adding the jobs that are currently not required, but adding your tool to help make sure this doesn't need as much maintenance in the future. That sounds interesting to me.