doc update : Updated the redirect path if user is not found (#22531)

Updated the redirect path if user is not found

Because the redirect path was `/` when I logged out and then went to something like `localhost:3000/` , this cause an infinite redirect loop and caused the app to break.

Co-authored-by: Charis <26616127+charislam@users.noreply.github.com>

apps/docs/content/guides/auth/server-side/nextjs.mdx

@@ -495,7 +495,7 @@ export default async function PrivatePage() {
 
   const { data, error } = await supabase.auth.getUser()
   if (error || !data?.user) {
-    redirect('/')
+    redirect('/login')
   }
 
   return <p>Hello {data.user.email}</p>