ci: lock closed issues after some time

Commenting on closed issues usually is not spotted by contributors or maintainers.
Meaning regressions will be overlooked and not fixed, so instead force people to open a new issue.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

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

@@ -0,0 +1,29 @@
+# SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+# SPDX-License-Identifier: MIT
+#
+# Commenting on closed issues usually is not spotted by contributors or maintainers.
+# Meaning regressions will be overlooked and not fixed, so instead force people to open a new issue.
+
+name: "Lock closed issues"
+
+on:
+  schedule:
+    - cron: "0 3 * * *" # every day at 03:00 UTC
+  workflow_dispatch:
+concurrency:
+  group: lock-threads
+permissions:
+  issues: write
+  pull-requests: write
+jobs:
+  lock:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: dessant/lock-threads@1bf7ec25051fe7c00bdd17e6a7cf3d7bfb7dc771 # v5.0.1
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          issue-inactive-days: 30
+          issue-comment: >
+            This issue has been automatically locked because it has been closed for 30 days.
+            Please open a new issue if you have a similar problem.