Clean up some type annotations in test/jit/...../test_class_type.py (#50156)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50156
Upgrades type annotations from Python2 to Python3
Test Plan: Sandcastle tests
Reviewed By: xush6528
Differential Revision: D25720035
fbshipit-source-id: 7e1aec34b21f3c9a3e8db9578258d99ffb87e6d4
