llvmbot removes manually-added labels on PRs

[ldionne]

For example, I manually added the libc++ label when I created #65344, but then llvmbot removed it immediately after.

[llvmbot]

@llvm/issue-subscribers-infrastructure

[cor3ntin]

I'll look into it, the pr labelling is something we added today, apparently it has some kinks

[cor3ntin]

This might be slightly tricky, I think i need to update to https://github.com/actions/labeler/releases/tag/v5.0.0-alpha.1 and of course the whole config format changed.

In the meantime, the bot only run on PR creation so if you add labels after the bot run, they are preserved.

[cor3ntin]

Simpler Fix #65395