Add simple backwards compatibility check for torch.package (#66739)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/65154, tests for backwards compatibility of torch.package by checking if packages that were created before can still be loaded.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66739
Reviewed By: suo
Differential Revision: D31771526
Pulled By: PaliC
fbshipit-source-id: ba8c652c647b94114a058e4c7d7f1c7ce6033d84
