ignoring *.cuh prevents multi_tensor_apply.cuh from being pushed

[LckyLke]

This:

https://github.com/deepspeedai/DeepSpeed/blob/53e91a098d0a0666ac8cb8025a5b36e5af172d08/.gitignore#L61C1-L61C6

ignores the multi_tensor_apply.cuh file which prevents fusedAdam from working when this file is not being pushed to remote, when working with a cloned copy of Deepspeed.