Add comment to workflow file (#13343)

.github/workflows/backport.yml

@@ -48,7 +48,14 @@ jobs:
 
           git checkout -b $branch
           git cherry-pick $commit
+
+          # note this push will fail if the backport contains any workflow files
+          # because secrets.GITHUB_TOKEN doesn't have this permission
+          # supporting this would require another access token with content write
+          # and workflow write permissions
+          # so for now at least PRs that update workflow files need to be backported manually
           git push --set-upstream origin $branch
+
           gh pr create --title "[$GITHUB_REF_NAME] $title" \
                        --body "Clean cherry-pick of #$NUMBER to the \`$GITHUB_REF_NAME\` branch." \
                        --base $GITHUB_REF_NAME