Auto merge of #29964 - mukilan:enable-merge-queue-action, r=mrobinson

Run main workflow for merge queue events

This PR configures the main workflow (currently used by bors via auto & try branches) to run
on 'merge_group' events emitted when pull requests are added to GitHub merge queue.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they just extend merge checks.

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.github/workflows/main.yml

@@ -4,6 +4,10 @@ on:
   push:
     branches: ["auto", "try"]
 
+  # Used by GH merge queue for landing PRs
+  merge_group:
+    types: [checks_requested]
+
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch: