Close stale pull requests

.github/workflows/stale.yml

@@ -0,0 +1,24 @@
+name: 'Close stale pull requests'
+on:
+  schedule:
+    - cron: '0 3 * * *'
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          stale-pr-message: >
+            There hasn't been any activity on this pull request in the past 90 days, so
+            it has been marked as stale and it will be closed automatically if no
+            further activity occurs in the next 7 days.
+
+            If you want to continue working on it, please leave a comment.
+
+          close-pr-message: >
+            This pull request was closed due to inactivity.
+
+          days-before-stale:    -1
+          days-before-pr-stale: 90
+          days-before-pr-close: 7