fix root context

Author: trueadm

packages/svelte/tests/runtime-legacy/samples/onmount-external/main.svelte

@@ -1,5 +1,13 @@
+<script module>
+	import { onMount } from 'svelte';
+
+	class MyClass {
+		constructor() {
+			onMount(() => console.log('mounted'));
+		}
+	}
+</script>
+
 <script>
-	import { MyClass } from "./myClass.js";
-	
 	new MyClass();
 </script>