Run Compiler tests in parallel for Pkg.test, continued

[serenity4]

Continues work on #56655, rebased onto current master.

[KristofferC]

Would also have been ok to just push to #56655 instead of creating a new PR and losing the comments etc. Anyway, I'll just close the old one.

[Keno]

Would also have been ok to just push to #56655 instead of creating a new PR and losing the comments etc. Anyway, I'll just close the old one.

@serenity4 doesn't have commit bit right now, so I told him to just go ahead and do a new one.

[KristofferC]

Makes sense, out of curiosity, what was wrong with #56655. CI seemed to pass and the comments were addressed AFAIU. If further things were needed I could just have fixed those as well..?

[Keno]

AFAICT we just lost track of it. I was trying to find it yesterday, but couldn't, so I asked @serenity4 to look into finishing it. I didn't remember what the status of it was. New PR is just for rebase purposes.

[KristofferC]

Ok, also possible to just rebase from the UI. 🤷 oh well.

[serenity4]

Besides rebasing and re-running CI, the intention was to be able to push changes if needed. But if all the work is actually done and tests pass so that nothing needs to be updated, that new PR would have been unnecessary indeed 😅 let's see.

[serenity4]

The test revise failure is unrelated (was observed in another PR: https://buildkite.com/julialang/julia-master/builds/46459#0195fa09-0417-4ca9-bc9c-b97173dc7cc7), I'm looking into the profiling failure.

[KristofferC]

That profiling test is known to be flaky.

[serenity4]

I guess we can merge these changes then. Given that I haven't contributed anything useful here, feel free to close this PR and reopen/merge #56655.

[KristofferC]

Commits are the same so it doesn't really matter what PR they come from :)