docs(svelte): fix vitest config file (#1159)

Author: mouse484

docs/svelte-testing-library/setup.mdx

@@ -37,7 +37,7 @@ with any testing framework and runner you're comfortable with.
 4.  Add a `vitest.config.ts` configuration file to the root of your project
 
     ```js
-    import { defineConfig } from 'vite';
+    import { defineConfig } from 'vitest/config';
     import { svelte } from '@sveltejs/vite-plugin-svelte';
 
     export default defineConfig({