fix: bump system test python versions in owlbot config

Author: abbrowne126

owlbot.py

@@ -340,8 +340,8 @@
     versions=gcp.common.detect_versions(path="./google", default_first=True),
     unit_test_python_versions=["3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"],
     unit_test_dependencies=["flaky"],
-    system_test_python_versions=["3.12"],
-    system_test_external_dependencies=["psutil","flaky"],
+    system_test_python_versions=["3.13"],
+    system_test_external_dependencies=["psutil", "flaky"],
 )
 s.move(templated_files, excludes=[".coveragerc", ".github/blunderbuss.yml", ".github/release-please.yml", "README.rst", "docs/index.rst"])