Tidying up auto-close-pr's yml

Author: mccaffers

.github/workflows/auto-close-external-prs.yml

@@ -3,11 +3,10 @@ name: "Auto-Close External PRs"
 on:
   pull_request_target:
     types: [opened]
-  workflow_dispatch:
 
 jobs:
   close-on-open:
-    if: github.event_name == 'pull_request_target' && github.event.pull_request.user.login != github.repository_owner
+    if: github.event.pull_request.user.login != github.repository_owner
     runs-on: ubuntu-latest
     permissions:
       pull-requests: write