Add a single commit check workflow

[daviddavis]

[noissue]

[daviddavis]

Stolen from Katello: https://github.com/Katello/katello/blob/master/.github/workflows/pull_request.yml

I'm imagining that this will be a non-blocking test. In other words, it won't prevent merges. It will just help to warn contributors/PR reviewers that there's more than one commit.

[bmbouter]

Awesome! Will this be enabled by default or do plugins need to opt-in? I'm +1 to enabling by default and opting out, but I'm ok w/ whatever you decide.

[daviddavis]

Thanks I forgot to set a default. I'm imagining it'll be enabled by default too.

[bmbouter]

I kind of liked the discourse announcement part. :) Thanks for doing this!

[daviddavis]

I kind of liked the discourse announcement part. :) Thanks for doing this!

Ha yea, that was a WIP I didn't mean to commit yet. Eventually I want to have the release automation automatically post the announcement to discourse.

[rochacbruno]

Nice! I will set it to false on galaxy_ng on next ci update.

We allow multiple commits because we enforce Squash and Merge.

[quba42]

I think I will also opt out pulp_deb. The PR volume is not so high that I feel the need to enforce single commits via automation.

[mdellweg]

Can this check be used to set/delete a "multiple commit" label on the PR, instead of presenting a failed test?

[daviddavis]

I think we could if we used a pull_request_target workflow. I personally like having a failing job as it's more obvious and shows near the merge button. But if you think we ought to use a label instead, I'd say open an issue, we can discuss more and I can look into it.