[CI] Use merge groups

[newling]

• Attempt to add merge trains / merge queues / merge groups to CI.
• The goal of this PR is to free developers from having to "Update branch" if a patch lands between them submitting a PR and CI passing:

• Nice description of how they work (gitlab equivalent): https://about.gitlab.com/blog/2020/01/30/all-aboard-merge-trains/#what-are-merge-trains-and-how-do-they-help%3F

• Based on PR from @stephenneuendorffer in mlir-aie: https://github.com/Xilinx/mlir-aie/pull/1461

[makslevental]

I have no idea how this works (will read the description soon) but I'm on board 🚆.

[newling]

It's one of those annoying PR's which you only know if it works after it's landed so here goes...