Add the unittest import for test_fake_quant.py (#28815)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28815
Add the unittest import
ghstack-source-id: 92789329
Test Plan: CI
Differential Revision: D18191989
fbshipit-source-id: c54e0309e21156c33e4fec01bfba17a1c30463c9
