Fix get_all_math_dtypes for device='cuda' retuning None (#23028)
Summary:
This PR fixes the invalid None return when calling get_all_math_dtype(device='cuda').
Issue came from the __append__ method which doesn't have any return value used in `return dtypes.append(...)`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23028
Differential Revision: D16362732
Pulled By: colesbury
fbshipit-source-id: 0bbc30a0c663749d768159f1bc37b99f7263297b
