checks requiring GPU moved to their own test (#25555)
Summary:
`test_allreduce_coalesced_checks` is skipped if no GPU/not compiled with `CUDA` support. This PR moves the checks involving `.cuda()` to their own tests, since the others are still valid with or without CUDA.
cc pietern mrshenli
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25555
Differential Revision: D17160337
Pulled By: pietern
fbshipit-source-id: 4c5e6db44d2728ca43784b85131e890d3d003bcd
