fix spreading of symbol properties onto component

packages/svelte/src/internal/client/reactivity/props.js

@@ -231,9 +231,14 @@ const spread_props_handler = {
 
 		for (let p of target.props) {
 			if (is_function(p)) p = p();
+
 			for (const key in p) {
 				if (!keys.includes(key)) keys.push(key);
 			}
+
+			for (const key of Object.getOwnPropertySymbols(p)) {
+				if (!keys.includes(key)) keys.push(key);
+			}
 		}
 
 		return keys;

packages/svelte/tests/runtime-runes/samples/attachment-component-spread/Child.svelte

@@ -0,0 +1,5 @@
+<script>
+	let props = $props();
+</script>
+
+<div {...props}></div>

packages/svelte/tests/runtime-runes/samples/attachment-component-spread/_config.js

@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+export default test({
+	ssrHtml: `<div></div>`,
+	html: `<div>set from component</div>`
+});

packages/svelte/tests/runtime-runes/samples/attachment-component-spread/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Child from './Child.svelte';
+
+	let stuff = $state({
+		[Symbol()]: (node) => node.textContent = 'set from component'
+	});
+</script>
+
+<Child {...stuff} />