Add 'cast' to import statements in collection.py

Author: daniel-sanche

packages/google-cloud-firestore/google/cloud/firestore_v1/collection.py

@@ -16,7 +16,7 @@
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Any, Callable, Generator, Optional, Tuple, Union
+from typing import TYPE_CHECKING, Any, Callable, Generator, Optional, Tuple, Union, cast
 
 from google.api_core import gapic_v1
 from google.api_core import retry as retries