Adding missing decorator for test_device_map_gpu_mixed_self_4 (#50732)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50732
Test Plan: Imported from OSS
Reviewed By: beauby
Differential Revision: D25954041
Pulled By: mrshenli
fbshipit-source-id: b2eeb1a77753cb8696613bfdc7bbc5001ae4c972
