Close all GitHub pull requests automatically.

Change-Id: Ie0849214f578b47d6da2a50205501f42b1572a52
Reviewed-on: https://code-review.googlesource.com/c/re2/+/59692
Reviewed-by: Jeff Bailey <[email protected]>
Reviewed-by: Paul Wankadia <[email protected]>

.github/workflows/pr.yml

@@ -0,0 +1,26 @@
+name: PR
+on:
+  pull_request:
+    branches: [main]
+    types: [opened]
+jobs:
+  close:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/github-script@v5
+        with:
+          script: |
+            const fs = require('fs');
+            console.log(await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              body: fs.readFileSync('CONTRIBUTING.md', { encoding: 'utf8', }),
+            }));
+            console.log(await github.rest.pulls.update({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: context.issue.number,
+              state: 'closed',
+            }));

CONTRIBUTING.md

@@ -1,2 +1,2 @@
 RE2 uses Gerrit instead of GitHub pull requests.
-See the [Contributing](https://github.com/google/re2/wiki/Contribute) wiki page.
+See the [Contribute](https://github.com/google/re2/wiki/Contribute) wiki page.