Clean up some type annotations in caffe2/test (#49943)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49943
Upgrades type annotations from Python2 to Python3
Test Plan: Sandcastle tests
Reviewed By: xush6528
Differential Revision: D25717534
fbshipit-source-id: 5aedea4db07efca126ffb6daee79617c30a67146
