ci: lock closed issues automatically after 90 days

[skip ci]

.github/workflows/stale.yml

@@ -0,0 +1,22 @@
+name: 'Lock old issues'
+
+on:
+  schedule:
+    - cron: '0 * * * *'
+  workflow_dispatch:
+
+permissions:
+  issues: write
+#  pull-requests: write
+#  discussions: write
+
+concurrency:
+  group: lock-threads
+
+jobs:
+  action:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v5
+        issue-inactive-days: 90
+        process-only: issues