chore: update one of the numbered list (#8134)

Author: bobbyu99

src/pages/[platform]/build-ui/formbuilder/index.mdx

@@ -91,7 +91,7 @@ Amplify.configure(outputs);
 import { TodoCreateForm } from './ui-components';
 ```
 
-3. Place your form in code. For a form named `ProductCreateForm` in a React project, you could use the following App code:
+4. Place your form in code. For a form named `ProductCreateForm` in a React project, you could use the following App code:
 
 ```jsx
 function App() {