internal: scheduler: add failing test for infinite onmount loop

This test shows how onMount is called repeatedly when creating a component dynamically.
The loop counter is totally arbitrary and is there to prevent a hard-crash in the CI.

test/runtime/samples/lifecycle-onmount-infinite-loop/Child.svelte

@@ -0,0 +1 @@
+Child

test/runtime/samples/lifecycle-onmount-infinite-loop/_config.js

@@ -0,0 +1,6 @@
+export default {
+	test({ assert, component }) {
+		const { count } = component;
+		assert.deepEqual(count, 1);
+	}
+};

test/runtime/samples/lifecycle-onmount-infinite-loop/main.svelte

@@ -0,0 +1,16 @@
+<script>
+	import { onMount } from 'svelte';
+	import Child from './Child.svelte';
+
+	let root;
+	export let count = 0;
+
+	onMount(() => {
+		if (count < 5) {
+			count++;
+			let child = new Child({target:root});
+		}
+	});
+</script>
+
+<div bind:this={root}></div>