Update rstest/rspack-adapter/src/main.tsx

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 9aoy

rstest/rspack-adapter/src/main.tsx

@@ -3,7 +3,11 @@ import ReactDOM from 'react-dom/client';
 import App from './App.tsx';
 import './index.css';
 
-ReactDOM.createRoot(document.getElementById('root') as HTMLElement).render(
+const rootElement = document.getElementById('root');
+if (!rootElement) {
+  throw new Error('Failed to find the root element');
+}
+ReactDOM.createRoot(rootElement).render(
   <React.StrictMode>
     <App />
   </React.StrictMode>,