fix typo in test_dataloader test_multiprocessing_contexts (take 2) (#43588)
Summary:
2nd attempt to land https://github.com/pytorch/pytorch/pull/43343
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43588
Reviewed By: seemethere
Differential Revision: D23332284
Pulled By: malfet
fbshipit-source-id: d78faf468c56af2f176dbdd2ce4bd51f0b5df6fd
