`onecold(:: OneHotMatrix(::CuArray), ::UnitRange)` uses scalar indexing

Surely this should just work:
```julia
julia> ytest
10×10000 OneHotMatrix(::CuArray{UInt32, 1, CUDA.Mem.DeviceBuffer}) with eltype Bool:
⋅ ⋅ ⋅ 1 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ 1 ⋅ ⋅ 1 ⋅ ⋅ … ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ 1 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅
⋅ ⋅ 1 ⋅ ⋅ 1 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ 1 ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ 1 ⋅ ⋅ ⋅ ⋅ ⋅
...

julia> onecold(ytest, 0:9)[5]
┌ Warning: Performing scalar indexing on task Task (runnable) @0x00007ff9074a4010.
│ Invocation of getindex resulted in scalar indexing of a GPU array.
│ This is typically caused by calling an iterating implementation of a method.
│ Such implementations *do not* execute on the GPU, but very slowly on the CPU,
│ and therefore are only permitted from the REPL for prototyping purposes.
│ If you did intend to index this array, annotate the caller with @allowscalar.
└ @ GPUArraysCore ~/.julia/packages/GPUArraysCore/lojQM/src/GPUArraysCore.jl:90
4
```