fixup: relative link

Author: mcous

docs/svelte-testing-library/faq.mdx

@@ -67,7 +67,7 @@ test('upload file', async () => {
 })
 ```
 
-[upload]: https://testing-library.com/docs/user-event/utility#upload
+[upload]: ../user-event/api-utility.mdx#upload
 [jsdom]: https://github.com/jsdom/jsdom
 [happy-dom]: https://github.com/capricorn86/happy-dom