ci: add CodeQL security scanning (weekly + on push/PR)

Author: lgutschow

.github/workflows/codeql.yml

@@ -0,0 +1,20 @@
+name: CodeQL
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: '0 6 * * 1'
+jobs:
+  analyze:
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+    steps:
+      - uses: actions/checkout@v6
+      - uses: github/codeql-action/init@v3
+        with:
+          languages: ruby
+      - uses: github/codeql-action/autobuild@v3
+      - uses: github/codeql-action/analyze@v3