Turn zzModRing & ZZModRing into ResidueRing subtypes

Since the element types of these ring types are subtypes of ResElem, the
rings should be subtypes of ResidueRing. Otherwise some generic code
gets confused (notably check_parent for ResElem).

This lead to a wrong error in the OSCAR book's introduction notebook.

src/flint/FlintTypes.jl

@@ -410,7 +410,7 @@ The ring $\mathbb Z/n\mathbb Z$ for some $n$. See [`residue_ring`](@ref).
 Implementation for the modulus being a machine integer [`Int`](@ref).
 For the modulus being a [`ZZRingElem`](@ref) see [`ZZModRing`](@ref).
 """
-@attributes mutable struct zzModRing <: Ring
+@attributes mutable struct zzModRing <: ResidueRing{UInt}
   n::UInt
   ninv::UInt
 
@@ -506,7 +506,7 @@ The ring $\mathbb Z/n\mathbb Z$ for some $n$. See [`residue_ring`](@ref).
 Implementation for the modulus being a big integer [`ZZRingElem`](@ref).
 For the modulus being an [`Int`](@ref) see [`zzModRing`](@ref).
 """
-@attributes mutable struct ZZModRing <: Ring
+@attributes mutable struct ZZModRing <: ResidueRing{ZZRingElem}
   n::ZZRingElem
   ninv::fmpz_mod_ctx_struct