Update faq.mdx - fix code block and formatting (#1473)

Author: dwjohnston

docs/react-testing-library/faq.mdx

@@ -113,6 +113,7 @@ test('error boundary catches error', () => {
  )
  expect(container.textContent).toEqual('Something went wrong.')
 })
+```
 
 If the error boundary did not catch the error, the test would fail since the `render` call would throw the error the Component produced.