ci: add cleanup step to Maven build process

Author: paul58914080

.github/workflows/ci.yaml

@@ -30,6 +30,8 @@ jobs:
             ${{ runner.os }}-maven-
       - name: Build with Maven
         run: mvn clean install -ntp
+      - name: Clean up
+        run: mvn clean
   generate-template:
     needs: example-ci
     runs-on: ubuntu-latest