Fix act() event example using button before declaration (#8593)

* Fix act() dispatch example using button before it is defined

The event example called button.dispatchEvent before const button was declared, which would throw at runtime. Also drop it.only from the docs snippet.

* Highlight the full act event-dispatch block

---------

Co-authored-by: Aurora Scharff <aurora.sofie@gmail.com>

Author: fbellinder

src/content/reference/react/act.md

@@ -117,26 +117,27 @@ Using `act` ensures that all updates have been applied before we make assertions
 
 To test events, wrap the event dispatch inside `act()`:
 
-```js {14,16}
+```js {17-19}
 import {act} from 'react';
 import ReactDOMClient from 'react-dom/client';
 import Counter from './Counter';
 
-it.only('can render and update a counter', async () => {
+it('can render and update a counter', async () => {
   const container = document.createElement('div');
   document.body.appendChild(container);
 
-  await act( async () => {
+  await act(async () => {
     ReactDOMClient.createRoot(container).render(<Counter />);
   });
 
+  const button = container.querySelector('button');
+  const label = container.querySelector('p');
+
   // ✅ Dispatch the event inside act().
   await act(async () => {
     button.dispatchEvent(new MouseEvent('click', { bubbles: true }));
   });
 
-  const button = container.querySelector('button');
-  const label = container.querySelector('p');
   expect(label.textContent).toBe('You clicked 1 times');
   expect(document.title).toBe('You clicked 1 times');
 });