cub::DeviceSelect::UniqueByKey might be ambiguous

` cub::DeviceSelect::UniqueByKey` might be ambiguous after the adding the env overloads.

- [ ] solve the ambiguity
- [ ] find out why wasn't it caught from tests

Candidate call that showcases the ambiguity:

```cpp
int* d_keys_in = nullptr;
int* d_values_in = nullptr;
int* d_keys_out = nullptr;
int* d_values_out = nullptr;
int* d_num_selected_out = nullptr;
int num_items = 0;

auto env = cuda::execution::require(cuda::execution::determinism::run_to_run);

auto a = cub::DeviceSelect::UniqueByKey(
d_keys_in, d_values_in, d_keys_out, d_values_out, d_num_selected_out, num_items, env);
```

@bernhardmgruber for viz