docs: resolve minor syntax error. (#22375)

Used the correct magic command. 
Changed from `% pip...` to `%pip`

Co-authored-by: Erick Friis <erick@langchain.dev>

docs/docs/tutorials/agents.ipynb

@@ -117,7 +117,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "% pip install -U langchain-community langgraph langchain-anthropic tavily-python"
+    "%pip install -U langchain-community langgraph langchain-anthropic tavily-python"
    ]
   },
   {