docs: Fixed incorrect tool in 'Write from tools' documentation (#4572)

I was having trouble following this section of the docs and I realized
it is because the incorrect tools is included in the tools list.
`update_user_info` was defined earlier in the file but never used.

docs/docs/agents/memory.md

@@ -282,7 +282,7 @@ def greet(
 
 agent = create_react_agent(
     model="anthropic:claude-3-7-sonnet-latest",
-    tools=[get_user_info, greet],
+    tools=[update_user_info, greet],
     # highlight-next-line
     state_schema=CustomState
 )
@@ -420,4 +420,4 @@ LangGraph also allows you to [search](https://langchain-ai.github.io/langgraph/h
 
 ## Additional resources
 
-* [Memory in LangGraph](../concepts/memory.md)
+* [Memory in LangGraph](../concepts/memory.md)