Docs: Incorrect status code used in authentication docs

### What is the documentation issue? I created a PR (#79974) to update this incorrect use of a 401 status code that I believe was wrongfully closed. The logic is clearly checking whether the user has the "admin" role and so would imply a 403 Forbidden response if they don't. Elsewhere in the docs, a 403 response is given for the same check ([see route handler docs](https://nextjs.org/docs/app/guides/authentication#route-handlers)), so one of them must be incorrect. ### Is there any context that might help us understand? N/A ### Does the docs page already exist? Please link to it. https://nextjs.org/docs/pages/guides/authentication#creating-a-data-access-layer-dal-1