Support the pull request policy by using github actions.

pragmatic bash code to close pull requests from forks

.github/workflows/pull_request.yml

@@ -0,0 +1,20 @@
+name: Pull request closer
+
+on:
+  pull_request_target:
+    types: [opened,reopened]
+jobs:
+  close-fork-pull-request:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.head.repo.full_name != github.repository
+    steps:
+      - name: close pull request
+        run: |
+          pull_request_id='${{ github.event.pull_request.number }}'
+          echo closing pull request "${pull_request_id}" in repository "${GITHUB_REPOSITORY}"
+          curl \
+          --request PATCH \
+          --header "Accept: application/vnd.github.v3+json" \
+          --header 'authorization: Bearer ${{ secrets.GITHUB_TOKEN }}' \
+          "${GITHUB_API_URL}/repos/${GITHUB_REPOSITORY}/pulls/${pull_request_id}" \
+          --data '{"state":"closed"}'