Enable merge queue

[terrytangyuan]

🚀 Describe the new functionality needed

Merge queue: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue

💡 Why is this needed? What if we don't build it?

This is to avoid the situation where CI would fail if an outdated PR is merged. Example: https://github.com/meta-llama/llama-stack/pull/1628

Other thoughts

No response