ci: enforce formatting

Author: Entenwilli

.github/workflows/main.yml

@@ -29,6 +29,8 @@ jobs:
           java-version: 17
       - name: Build and Verify
         run: mvn clean verify
+      - name: Check formatting
+        run: mvn spotless:check
       - name: Publish Nightly Update Site
         if: github.event_name != 'release' && github.ref == 'refs/heads/main' && github.repository_owner == 'DataFlowAnalysis'
         uses: peaceiris/actions-gh-pages@v4