Add testing to workflow

.github/workflows/gradle.yml

@@ -33,6 +33,9 @@ jobs:
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew
       
+    - name: Test with Gradle
+      run: ./gradlew clean test
+      
     - name: Build with Gradle
       run: ./gradlew clean serverJar