Add workflow_dispatch so we can run manually (#9253)

.github/workflows/stale.yml

@@ -1,7 +1,8 @@
 name: Close Stale Issues
 on:
   schedule:
-  - cron: '0 12 * * *'
+    - cron: '0 12 * * *'
+  workflow_dispatch:
 jobs:
   stale:
     runs-on: ubuntu-latest