fix: set merge conflict Action to run every 12 hours instead of every 15 minutes (#39335)

* fix: run action every 12 hours

Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

.github/workflows/label_merge_conflicts.yml

@@ -1,8 +1,8 @@
 name: 'Check for merge conflicts'
 on:
   schedule:
-    # run this Action every 15 minutes
-    - cron:  '*/15 * * * *'
+    # run this Action every 12 hours
+    - cron:  '0 */12 * * *'
 jobs:
   triage:
     runs-on: ubuntu-18.04