[Internal] Add comment to validate workflow (#987)

## Changes
Add comment to validate workflow

.github/workflows/message.yml

@@ -9,6 +9,9 @@ on:
 jobs:
   validate:
     runs-on: ubuntu-latest
+    # GitHub required checks are shared between PRs and the Merge Queue.
+    # Since there is no PR title on Merge Queue, we need to trigger and
+    # skip this test for Merge Queue to succeed.
     if: github.event_name == 'pull_request' 
     steps:
       - name: Checkout