docs(tutorial): fix syntax err in composition slot prop app-a

documentation/tutorial/14-composition/05-slot-props/app-a/App.svelte

@@ -1,5 +1,6 @@
 <script>
 	import Hoverable from './Hoverable.svelte';
+	let hovering = false;
 </script>
 
 <Hoverable>

documentation/tutorial/14-composition/05-slot-props/app-a/Hoverable.svelte

@@ -10,6 +10,6 @@
 	}
 </script>
 
-<div on:mouseenter={enter} on:mouseleave={leave}>
+<div on:mouseenter={enter} on:mouseleave={leave} role="banner">
 	<slot />
 </div>