[workflow] Use automerge_scan instead of automerge for correct commit message. (#17669)

Why I did it
automerge and automerge_scan have different behavior when merging PRs.
automerge may left some PRs unmerged. So, use automerge_scan instead.

Work item tracking
Microsoft ADO (number only): 26361240
How I did it
How to verify it

Author: liushilongbuaa

.github/workflows/automerge.yml

@@ -9,7 +9,8 @@ on:
 
 jobs:
   automerge:
-    if: github.event.check_suite.app.name == 'Azure Pipelines' &&  github.event.check_suite.conclusion == 'success'
+    # Disable workflow. Use automerge_scan instead to have the same behaviour.
+    if: github.event.check_suite.app.name == 'Azure Pipelines' &&  github.event.check_suite.conclusion == 'success' && false
     runs-on: ubuntu-latest
     steps:
     - name: automerge