style: fix mypy issue (#1425)

astronomer/providers/google/cloud/gke_utils.py

@@ -9,7 +9,7 @@
 from airflow.exceptions import AirflowException
 from airflow.providers.google.common.hooks.base_google import GoogleBaseHook
 from airflow.utils.process_utils import execute_in_subprocess, patch_environ
-from google.auth import impersonated_credentials
+from google.auth import impersonated_credentials  # type: ignore[attr-defined]
 from google.cloud.container_v1 import ClusterManagerClient
 from google.oauth2.service_account import Credentials
 from kubernetes_asyncio.config.kube_config import KubeConfigLoader