Python 3.9 support

Author: cpsievert

pkg-py/src/shinychat/_chat_normalize_chatlas.py

@@ -2,11 +2,13 @@
 import os
 import warnings
 from dataclasses import dataclass
-from typing import TYPE_CHECKING, Literal, TypeGuard
+from typing import TYPE_CHECKING, Literal
 
 from htmltools import RenderedHTML, Tag, TagChild, Tagifiable, TagList
 from packaging import version
 
+from ._typing_extensions import TypeGuard
+
 if TYPE_CHECKING:
     from chatlas.types import ContentToolRequest, ContentToolResult