Revert "chore: add manual trigger"

This reverts commit af9517f.

Author: rjan90

.github/workflows/stale.yml

@@ -2,8 +2,7 @@ name: Mark and close stale items
 
 on:
   schedule:
-    - cron: '0 12 * * *'
-  workflow_dispatch:
+  - cron: '0 12 * * *'
 
 permissions:
   contents: read