prePR command—or another solution to fatal-warnings-in-CI

[armanbilge]

Spinning out of #12 (comment).

The underlying problem is we often want fatal warnings in CI, but not locally since it makes development/experimentation annoying. But then, we end up fighting CI :)

One proposal is we add a prePR command that emulates a CI compile, by cleaning and enabling fatal warnings (if that is indeed how CI is configured).

[armanbilge]

Ooh, another good one for prePR is to check the workflow is up-to-date. I just mucked that up.