Check source code format

Author: backpaper0

.github/workflows/ci.yml

@@ -29,7 +29,7 @@ jobs:
         run: chmod +x mvnw
 
       - name: Test with Maven
-        run: ./mvnw $MAVEN_CLI_OPTS test
+        run: ./mvnw $MAVEN_CLI_OPTS formatter:validate test
 
       - name: Upload reports
         if: failure()