Mark Data.Text.Internal as Safe Haskell

E.g. [Simon Marlow said to me](https://github.com/simonmar/async/issues/151#issuecomment-1770564572)

> I think you might have a different interpretation of "Module encapsulation" than the intended one. Safe Haskell only promises that the semantics of abstraction are respected, it doesn't promise that you can't see the representation of a datatype by importing it from some other module.

So I don't see a reason for `Data.Text.Internal` to not be marked as Trustworthy module. E.g. `containers` [`Data.Set.Internal`](https://hackage.haskell.org/package/containers-0.7/docs/Data-IntSet-Internal.html) is trustworthy. And I'd expect that libraries bundles with GHC do the Safe Haskell stuff the same (and right) way if they have any Safe Haskell annotations at all.