fix: prevent access of Svelte 5-only untrack function (#14658)

Fixes #14657

Author: dummdidumm

.changeset/thick-ideas-mate.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: prevent access of Svelte 5-only `untrack` function

packages/kit/src/runtime/form-utils.svelte.js

@@ -3,7 +3,9 @@
 /** @import { StandardSchemaV1 } from '@standard-schema/spec' */
 
 import { DEV } from 'esm-env';
-import { untrack } from 'svelte';
+import * as svelte from 'svelte';
+// Svelte 4 and under don't have `untrack` - you'll not be able to use remote functions with Svelte 4 but this will still be loaded
+const untrack = svelte.untrack ?? ((value) => value());
 
 /**
  * Sets a value in a nested object using a path string, not mutating the original object but returning a new object