allow root params access in private caches (#82125)
Accessing root params in a private cache should work, but I missed it in
the `next/root-params` PR.
```tsx
import { lang } from 'next/root-params'
async function foo() {
'use cache: private'
await lang() // this is okay
}
```
With this PR, we'll now allow this (and `unstable_rootParams()`)
