Fix skip_if_not_multigpu decorator (#54916)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54916
Fixes https://github.com/pytorch/pytorch/issues/54887
`skip_if_not_multigpu` was skipping all the tests that use it.
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D27412193
Pulled By: H-Huang
fbshipit-source-id: 28d6697bd8cc6b6784cdb038ccb3ff138d0610eb
