[llvm] [GitHub][workflows] Ask reviewers to merge PRs when author cannot (PR #81142)

[David Spickett via llvm-commits]

DavidSpickett wrote:

Fixed. We now pass the PR author (to check for merge permissions) and review author (to address the comment to) to the automation script.

It's possible the reviewer doesn't have permissions either. We can check this too but I'm wondering what would be useful to say in that scenario. Perhaps `@foo the author of this PR does not have permission to merge PRs, and neither do you. Please find someone who can merge on the author's behalf.`.

Then the obvious follow up is how do they find someone to merge it, discord is probably the best place?

https://github.com/llvm/llvm-project/pull/81142