Add support for merge queues (#6953)

Per instructions on the following pages, adding a `merge_group` trigger
is needed to use merge queues.

-
https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue#triggering-merge-group-checks-with-github-actions
-
https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#merge_group

Author: mhucka

.github/workflows/ci.yml

@@ -7,6 +7,9 @@ on:
   pull_request:
     branches:
       - main
+  merge_group:
+    types:
+      - checks_requested
 
 concurrency:
   group: ${{ github.head_ref || github.run_id }}