refactor(numpydates): add concrete type check for inline datetime/timedelta types

Ensure that type T is concrete before checking if it subtypes the union of InlineDateTime64 and InlineTimeDelta64, preventing potential issues with abstract types in pytypestrdescr function.

Author: Christopher Doris

src/JlWrap/array.jl

@@ -267,7 +267,8 @@ pytypestrdescr(::Type{T}) where {T} =
             ("$(c)c8", PyNULL)
         elseif T == Complex{Float64}
             ("$(c)c16", PyNULL)
-        elseif T <: Union{NumpyDates.InlineDateTime64,NumpyDates.InlineTimeDelta64}
+        elseif isconcretetype(T) &&
+               T <: Union{NumpyDates.InlineDateTime64,NumpyDates.InlineTimeDelta64}
             u, m = NumpyDates.unitpair(T)
             tc = T <: NumpyDates.InlineDateTime64 ? 'M' : 'm'
             us =