Fix typing on nn.Parameter (#25586)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/25399
As per https://github.com/pytorch/pytorch/issues/25580 I'm pushing this to test my changes on the CI
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25586
Differential Revision: D17259178
Pulled By: ezyang
fbshipit-source-id: d48cdd602bfda60c213f79a4f124df54a68ca698
