add lock inactive closed issues workflow

.github/workflows/lock.yaml

@@ -0,0 +1,25 @@
+name: 'Lock inactive closed issues'
+# Lock closed issues that have not received any further activity for two weeks.
+# This does not close open issues, only humans may do that. We find that it is
+# easier to respond to new issues with fresh examples rather than continuing
+# discussions on old issues.
+
+on:
+  schedule:
+    - cron: '0 0 * * *'
+
+permissions:
+  issues: write
+  pull-requests: write
+
+concurrency:
+  group: lock
+
+jobs:
+  lock:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@c1b35aecc5cdb1a34539d14196df55838bb2f836
+        with:
+          issue-inactive-days: 14
+          pr-inactive-days: 14