meta: remove never-used workflow trigger

PR-URL: https://github.com/nodejs/node/pull/54983
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>

.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