chore(python_mono_repo): add python runtimes for system tests (#1869)

Author: parthea

synthtool/languages/python_mono_repo.py

@@ -158,6 +158,7 @@ def owlbot_main(package_dir: str) -> None:
             microgenerator=True,
             default_python_version="3.9",
             unit_test_python_versions=["3.7", "3.8", "3.9", "3.10", "3.11"],
+            system_test_python_versions=["3.8", "3.9", "3.10", "3.11"],
             cov_level=100,
             versions=gcp.common.detect_versions(
                 path=f"{package_dir}/google",