Bug 1847997: Automatically close GitHub pull requests with a GitHub Action r=hwine DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D185836

.github/workflows/README

@@ -0,0 +1,7 @@
+IMPORTANT
+
+All changes and/or additions to GitHub Workflows MUST be approved by the
+Mozilla GitHub Enterprise Administrators Team.
+
+See https://mozilla-hub.atlassian.net/l/cp/f5ypVsa7 for contact information, or
+reach out on Matrix: https://chat.mozilla.org/#/room/#github-admin:mozilla.org

.github/workflows/close-pr.yml

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+name: close pull request
+on:
+  pull_request:
+    types: [opened, reopened]
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v3
+      - name: close
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          PR=$(echo "$GITHUB_REF" | awk 'BEGIN { FS = "/" } ; { print $3 }')
+          gh pr close $PR --comment "(Automated Close) Please do not file pull requests here, see https://firefox-source-docs.mozilla.org/contributing/how_to_submit_a_patch.html"
+          gh pr lock $PR