Fix Python 3.9 compatibility for union type hint

Author: fede-kamel

libs/oci/tests/integration_tests/chat_models/test_gemini_tool_calling.py

@@ -40,7 +40,7 @@
 from langchain_oci.chat_models import ChatOCIGenAI
 
 
-def _content_to_str(content: str | list) -> str:
+def _content_to_str(content: "str | list") -> str:
     """Convert message content to string for assertions.
 
     AIMessage.content can be str or list[str | dict], so we need to