refactor: ♻️ fix vitest config

Author: spences10

packages/sveltekit-embed/vite.config.ts

@@ -1,8 +1,9 @@
 import { sveltekit } from '@sveltejs/kit/vite';
+import { svelteTesting } from '@testing-library/svelte/vite';
 import { defineConfig } from 'vitest/config';
 
 export default defineConfig({
-	plugins: [sveltekit()],
+	plugins: [sveltekit(), svelteTesting()],
 	test: {
 		environment: 'jsdom',
 		include: ['src/**/*.{test,spec}.{js,ts}'],