chore: restore import CrossSync

Author: chalmerlowe

packages/google-cloud-spanner/google/cloud/spanner_v1/snapshot.py

@@ -21,6 +21,7 @@
 from typing import List, Optional, Union
 
 from google.api_core import gapic_v1
+from google.cloud.aio._cross_sync import CrossSync
 from google.api_core.exceptions import (
     Aborted,
     InternalServerError,