ci(ci.yml): Add renovate-config-validator to validate presets

Author: flovogt

.github/workflows/ci.yml

@@ -29,3 +29,6 @@ jobs:
 
     - name: Perform dependency check
       run: npm run knip
+
+    - name: Perform Renovate config validation
+      run: npx --yes --package renovate -- renovate-config-validator --no-global --strict datasources.json default.json lts.json