Create lock-closed-issues.yml

Added new workflow for locking closed issues, pull requests and discussions.

.github/workflows/lock-closed-issues.yml

@@ -0,0 +1,26 @@
+name: 'Lock closed issues'
+# Workflow that automatically locks already closed issues,
+# pull requests and discussions.
+
+on:
+  schedule:
+    - cron: '30 6 * * *'
+  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
+        with:
+          issue-inactive-days: 21
+          pr-inactive-days: 28
+          discussion-inactive-days: 28