force javadoc check in CI build

Author: yuzawa-san

.github/workflows/tests.yml

@@ -28,7 +28,7 @@ jobs:
         languages: java
     - name: Build with Maven
       timeout-minutes: 15
-      run: mvn -B clean package --file pom.xml
+      run: mvn -B clean javadoc:javadoc package --file pom.xml
     - name: Perform CodeQL Analysis
       uses: github/codeql-action/analyze@v3
       with: