chore: update demo, and try codecov

Author: Feng Shang

.github/workflows/build.yml

@@ -23,4 +23,4 @@ jobs:
       run: mvn -B package --file pom.xml
 
     - name: Upload coverage reports to Codecov with GitHub Action
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v2