add workflow trigger for "Update Labels" to summarize-checks (#36530)

Author: scbedd

.github/workflows/summarize-checks.yaml

@@ -9,6 +9,7 @@ on:
       - "Swagger Avocado - Set Status"
       - "Swagger LintDiff - Set Status"
       - "SDK Validation Status"
+      - "Update Labels"
     types:
       - completed
   pull_request_target: # when a PR is labeled. NOT pull_request, because that would run on the PR branch, not the base branch.