chore(dependency-auto-merge): adjust triggers to reflect ruleset

Since this workflow is now required as part of an org-wide ruleset, we no longer need synced workflow files and can remove the workflow_call trigger.

.github/workflows/dependency-auto-merge.yml

@@ -1,7 +1,9 @@
+# This workflow is required and run as part of an org-wide ruleset
+
 name: Dependency Auto-Merge
 on:
-  workflow_call:
   pull_request:
+  merge_group:
 
 jobs:
   dependabot: