Better split of the windows test jobs (#50660)
Summary:
See discussion in https://github.com/pytorch/pytorch/pull/50320#discussion_r554447365.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50660
Reviewed By: xuzhao9, samestep
Differential Revision: D25959021
Pulled By: seemethere
fbshipit-source-id: 7623bddc09e7d55208b8a1af4b5a23fba2cdeb14
