Make the CI enforce make checkstyle clean code

Author: hartwork

.github/workflows/checkstyle.yml

@@ -0,0 +1,54 @@
+#
+#   Copyright (c) 2026 Sebastian Pipping <sebastian@pipping.org>
+#
+#   This program is free software;  you can redistribute it and/or modify
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation; either version 2 of the License, or (at
+#   your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY;  without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+#   General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with this program;  if not, see
+#   <http://www.gnu.org/licenses/>.
+#
+name: Enforce checkstyle-clean code
+
+on:
+  pull_request:
+  push:
+  schedule:
+    - cron: '0 14 * * 5'  # Every Friday 2pm
+  workflow_dispatch:
+
+# Drop permissions to minimum for security
+permissions:
+  contents: read
+
+jobs:
+  checkstyle:
+    name: Enforce checkstyle-clean code
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Install perltidy
+        run: |-
+          set -x
+          sudo apt-get update
+          sudo apt-get install --yes -V --no-install-recommends \
+              cpanminus
+
+          # NOTE: We install a pinned version to ensure robust CI
+          sudo cpanm --notest \
+              https://github.com/perltidy/perltidy/archive/refs/tags/20260705.01.tar.gz
+
+      - uses: actions/checkout@v7
+
+      - name: Enforce "make checkstyle"
+        run: |-
+          set -x
+          perltidy --version | grep -o 'v2.*'
+
+          MODE=full make checkstyle