Add file extension validation

.github/workflows/yaml-linting.yml

@@ -7,6 +7,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
+      - name: Check file extensions
+        run: if [[ $(find ./yml -type f -not -name "*.yml") ]]; then echo "Files with unexpected extension found, please ensure you use ".yml" (all lower case) for files in the yml/ folder."; exit 1; fi
       - name: yaml-lint
         uses: ibiqlik/action-yamllint@v3
         with: