fix for 3.9

tests/models/test_gemini.py

@@ -3,12 +3,12 @@
 import json
 from collections.abc import Awaitable, Callable
 from dataclasses import dataclass
-from typing import TypeAlias
 
 import httpx
 import pytest
 from inline_snapshot import snapshot
 from pydantic import BaseModel
+from typing_extensions import TypeAlias
 
 from pydantic_ai import Agent, AgentError, ModelRetry, UnexpectedModelBehaviour, UserError
 from pydantic_ai._utils import ObjectJsonSchema