install python3-virtualenv

Author: JoeWang1127

.cloudbuild/library_generation/cloudbuild-library-generation-integration-test.yaml

@@ -48,7 +48,7 @@ steps:
       apt-get update
       apt-get -y install \
         docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin \
-        maven
+        maven python3-virtualenv
       # Install python dependencies
       python3 -m venv .venv
       source .venv/bin/activate