update link to use public video instead of unlisted

apps/docs/pages/guides/auth/auth-helpers/nextjs.mdx

@@ -696,7 +696,7 @@ Check out the [Next.js auth example repo](https://github.com/supabase/supabase/t
 
 <div className="video-container">
   <iframe
-    src="https://www.youtube-nocookie.com/embed/B5TUzTKO9CE"
+    src="https://www.youtube-nocookie.com/embed/4_epZIxqCho"
     frameBorder="1"
     allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
     allowFullScreen