docs(09-authentication): fixes link to NextAuth.js (#64457)

There's a TODO above the links, I didn't understand if it was related to
this PR as the domain was already authjs.dev

### What?

- Fixes the link to NextAuth in the `Examples` section

### How?

- Changes https://authjs.dev/guides/upgrade-to-v5 to
https://authjs.dev/getting-started/migrating-to-v5

Co-authored-by: JJ Kasper <[email protected]>

Author: 2 people

docs/02-app/01-building-your-application/09-authentication/index.mdx

@@ -877,7 +877,7 @@ Here are authentication solutions compatible with Next.js, please refer to the q
 - [Clerk](https://clerk.com/docs/quickstarts/nextjs)
 - [Kinde](https://kinde.com/docs/developer-tools/nextjs-sdk)
 - [Lucia](https://lucia-auth.com/getting-started/nextjs-app)
-- [NextAuth.js](https://authjs.dev/guides/upgrade-to-v5)
+- [NextAuth.js](https://authjs.dev/getting-started/migrating-to-v5)
 - [Supabase](https://supabase.com/docs/guides/getting-started/quickstarts/nextjs)
 - [Stytch](https://stytch.com/docs/guides/quickstarts/nextjs)
 - [Iron Session](https://github.com/vvo/iron-session)