Switch React.Fragment out for span

This will make the DOM easier to reason about and a clearer 1:1 mapping.
Then I also don't gloss over the `</>` part.

Hat tip to C. Lates.

pages/react/getting-started.mdx

@@ -559,7 +559,7 @@ Go back to `App.tsx` and change the content to:
 
 <CodeFile language="tsx" file="App.tsx">
   {`
-const App = () => <>Hello World</>
+const App = () => <span>Hello World</span>
 export default App
 `}
 </CodeFile>