docs: Improve formatting consistency in structured outputs documentation

docs/core_docs/docs/concepts/structured_outputs.mdx

@@ -91,7 +91,7 @@ const model = new ChatOpenAI({
 });
 
 // Create a tool with ResponseFormatter as its schema.
-const responseFormatterTool =  tool(() => {},{ name : "responseFormatter", schema : ResponseFormatter })
+const responseFormatterTool =  tool(() => {},{ name: "responseFormatter", schema: ResponseFormatter })
 
 // Bind the created tool to the model
 const modelWithTools = model.bindTools([responseFormatterTool]);