[PyTorch] TensorIterator::output should return const reference (#54811)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54811
Callers can make a refcount bump themselves if they need one.
ghstack-source-id: 125136516
Test Plan: CI
Reviewed By: ngimel
Differential Revision: D27377210
fbshipit-source-id: ea58c7190fe2d7896432e403ecb1c59761aa319d
