ci: Change contributors workflow trigger from push to manual dispatch.

Author: tw93

.github/workflows/update-contributors.yml

@@ -1,8 +1,7 @@
 name: Update Contributors
 
 on:
-  push:
-    branches: [main, dev]
+  workflow_dispatch:
   schedule:
     - cron: "0 0 * * 0" # Every Sunday at midnight UTC