Enable GHA sharding on linux (#60124)
Summary:
This is branch off of https://github.com/pytorch/pytorch/issues/59970 to only shard on linux so far (we're running in issues with windows gflags).
This would enable sharding of tests on a few Linux jobs on GHA, allowing tts to be essentially halved.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60124
Reviewed By: zou3519
Differential Revision: D29204211
Pulled By: janeyx99
fbshipit-source-id: 1cc31d1eccd564d96e2aef14c0acae96a3f0fcd0
