Close PRs from non-collaborators

Author: prcwiek

.github/workflows/close-unknown.yml

@@ -0,0 +1,14 @@
+name: Close PRs from non-collaborators
+on:
+  pull_request_target:
+    types: [opened]
+
+jobs:
+  close-unauthorized:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Close PR
+        uses: superbrothers/close-pull-request@v3
+        with:
+          comment: "Thank you for your interest! We currently only accept PRs from invited collaborators."
+        if: github.event.pull_request.author_association == 'NONE'