Automatically label and milestone completions

[mqudsi]

This automatically assigns the 'completions' label and the 'fish next-3.x' milestone to completions-only PRs. Follow-up to #10515

A completions-only PR is defined as being one that touches share/completions/*.fish but does not touch any files outside of share/

We might want to update this to add an allow for CHANGELOG.rst in the future as well, but most PRs are without it because we didn't like how often that caused merged conflicts.

Tested on my own repo, you can see this sample PR that caused the GitHub actions bot to add the 'completions' label and the 'fish next-3.x' milestone label: mqudsi#4

[krobelus]

sounds fine. We could also delete the completions label entirely, I don't think it's used.

This is what I use:

gh pr edit "$url" --add-label completions
gh pr edit "$url" --milestone "$milestone"
gh pr merge --rebase "$url"

[mqudsi]

We could also delete the completions label entirely, I don't think it's used.

We (ok, mainly @zanchey) use it to find completions for changelog fixes and release notes. Also for backporting changes to minor releases (though that can probably be done easier with a command line git log -- 'share/completions/*' filter).

If it's applied automatically, it also goes from being a chore to being an asset. If a completion PR is opened but it doesn't have the label, then someone did something wrong and it's touching more files than it should.

[krobelus]

yeah I think git log is easier and more correct