docs: adjust Caching data with an ORM or Database section (#76454)
## Why?
Adjust first sentence of [Caching with an ORM or Database](https://nextjs.org/docs/app/building-your-application/data-fetching/fetching#caching-data-with-an-orm-or-database) section to clarify that you don't need `unstable_cache` to prerender a page.
- Fixes https://github.com/vercel/next.js/issues/73808