docs(react-dom): add expected error annotation for Math.random hydration example

Author: yogayataverma

src/content/reference/react-dom/client/hydrateRoot.md

@@ -552,11 +552,10 @@ Uncaught Error: Hydration failed because the server rendered HTML didn't match t
 
 #### Example mismatch {/*example-mismatch*/}
 
-```js
+```js {expectedErrors: {'react-compiler': [2]}}
 function App() {
   return <div>{Math.random()}</div>;
 }
-```
 
 This renders a different value on the server and the client, so hydration fails.