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 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
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