meta: remove never-used workflow trigger

PR-URL: nodejs#54983
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Marco Ippolito <[email protected]>

Author: avivkeller

.github/workflows/label-flaky-test-issue.yml

@@ -2,7 +2,7 @@ name: Label Flaky Test Issues
 
 on:
   issues:
-    types: [opened, labeled]
+    types: [labeled]
 
 permissions:
   contents: read