add each-block-keyed-iife test against regression (#3436)

test/runtime/samples/each-block-keyed-iife/_config.js

@@ -0,0 +1,7 @@
+export default {
+	html: `
+		<div>1</div>
+		<div>2</div>
+		<div>3</div>
+	`
+};

test/runtime/samples/each-block-keyed-iife/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	const arr = [1, 2, 3];
+</script>
+
+{#each arr as item ((() => item)())}
+	<div>
+		{item}
+	</div>
+{/each}