Convert assert -> cast. (#57458)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/55868.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57458
Reviewed By: mruberry
Differential Revision: D28365745
Pulled By: walterddr
fbshipit-source-id: 35cc3fa85f87b0ef98cf970f620ab909d240c7be
