[FEA] drop `typedef` in `cuda::atomic` test

[miscco]

    using A = cuda::atomic_ref<T, ThreadScope>;

Originally posted by @fbusato in #3440

[viralbhadeshiya]

I can take care of this, can someone assign this to me. Thanks.

[viralbhadeshiya]

@miscco can you assign this to me, or can I just start working?

[miscco]

you can always just work on something that interests you.