[PyTorch] Add unit test for c10::Synchronized<T> (#74110)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74110
Since this class was added, it's missing a unit test. dbort first noticed it, so adding one in this commit.
ghstack-source-id: 151471746
Test Plan: `buck test //xplat/caffe2/c10:c10_test`
Reviewed By: dbort
Differential Revision: D34822911
fbshipit-source-id: 919a125081a2093d6f4e5a2cdb008145c05ec803
(cherry picked from commit 358b7dacced866c54b8c1972393d042ebbd93d9e)
