Fix import in svelte-vite code example (#1312)

Author: andnorda

docs/svelte-testing-library/setup.mdx

@@ -49,7 +49,7 @@ npm install --save-dev @vitest/ui
 3. 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({