Fix typo in gradio-tools docs (#23305)

Fix typo

docs/source/en/custom_tools.mdx

@@ -726,7 +726,7 @@ We pass that instance to the `Tool.from_gradio` method:
 ```python
 from transformers import Tool
 
-tool = Tool.from_gradio(gradio_tools)
+tool = Tool.from_gradio(gradio_tool)
 ```
 
 Now we can manage it exactly as we would a usual custom tool. We leverage it to improve our prompt