[Github] Enable "require resolved" for auto-merge

Hello!

Would it be possible to require comments to be resolved to allow merging?
Example: https://github.com/llvm/offload-test-suite/pull/647

- Enabled auto-merge
- Steven had minor nits, but approved, so I could fix those & merge without having to wait for another cross-timezone review.
- because it had automerge, the PR for merged even with unresolved comments.