Notify PR authors of merge issues.

[PatrikLundell]

Is your feature request related to a problem? Please describe.

I'm always frustrated when checking back on a PR that somehow is left lingering and not being merged only to find that the time in the freezer has caused merge conflicts to creep up on it without me being notified about it.

To make it worse, the merge conflict info is hidden away below the test section, so if you keep a window open on the PR and check on it regularly, you may miss it, because you look for the test results and the comment section.

Solution you would like.

Primary: Send a message when a merge conflict is generated (bonus NOT to send a hail of redundant messages when tests are cancelled due to PR updates. You should already know it will happen, and you can't take any useful action upon getting the notice anyway).

Secondary: Move the merge conflict section to above the test section in the PR so you have a lower risk of missing it.

Describe alternatives you have considered.

No response

Additional context

No response

[moxian]

There's a lot of complaints on the internets about the issue, and about a lack of any solutions.
There's this gha runner that's supposed to fix it which might or might not run out of the box https://github.com/nokamoto/merge-conflict-action
I'm concerned that 1) i haven't found any references to it in any of the complaint threads (it's just a google result) and 2) the required repo var is kinda sus, and i don't understand what would it even do/why specify it.

That said, it's probably a good idea, and if someone can build/test it and make sure that it works, then we can probably install it here.