Run 'checkout' before 'setup ci environment' on pytorch linux tests (#20213)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20213
ghimport-source-id: ea395ee1151207f37e030ed0126564ff7a73bac8
Reviewed By: ezyang
Differential Revision: D15244428
Pulled By: zou3519
fbshipit-source-id: 45ba2a80a2a9d056f806b5960bfe20f3c60f1e33
