fix pytype

Change-Id: Ic5c250f3f3ded2374abfbdbee6d62ea4cfb0f799

Author: MarkDaoust

google/generativeai/client.py

@@ -3,6 +3,7 @@
 import os
 import contextlib
 import inspect
+import collections
 import dataclasses
 import pathlib
 from typing import Any, cast