Update act() usage to be async in examples

The second example uses a synchronous callback to act(), but the docs recommend always using the async version and mention the sync form will be deprecated.

This PR updates the example so the callback is async for consistency with current React recommendations.

Author: valgaze

src/content/reference/react/act.md

@@ -98,7 +98,7 @@ it('can render and update a counter', async () => {
   document.body.appendChild(container);
 
   // ✅ Render the component inside act().
-  await act(() => {
+  await act(async () => {
     ReactDOMClient.createRoot(container).render(<Counter />);
   });
 
@@ -126,7 +126,7 @@ it.only('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 />);
   });