Fix clang-tidy to run on the merge queue

Without this, the merge queue blocks on results but they never get
triggered and show up. This will need to merge before we re-enable
`clang-tidy` enforcement on the trunk branch.

.github/workflows/clang_tidy.yaml

@@ -8,6 +8,7 @@ on:
   push:
     branches: [trunk, action-test]
   pull_request:
+  merge_group:
 
 permissions:
   contents: read # For actions/checkout.