[PyTorch] Fix missing move in unpickler (#63974)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63974
Saw some time spent in this for model loading, no reason not to move here.
ghstack-source-id: 136760979
Test Plan: Re-profile model loading on devserver; IValue copy ctor time has gone down
Reviewed By: dhruvbird
Differential Revision: D30548923
fbshipit-source-id: 42000f2e18582762b43353cca10ae094833de3b3
