chore: restrict internet access when running docker container in integration test (#3384)

A verification step in go/offline-gen-design

Author: JoeWang1127

hermetic_build/library_generation/tests/integration_tests.py

@@ -303,6 +303,8 @@ def __run_entry_point_in_docker_container(
                 f"{user_id}:{group_id}",
                 "--rm",
                 "--quiet",
+                "--network",
+                "none",
                 "-v",
                 f"{repo_location}:/workspace/repo",
                 "-v",