Refactor backward compatibility tests to use override_qengines decorator (#38838)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/38838
Test Plan: Imported from OSS
Differential Revision: D21676032
Pulled By: durumu
fbshipit-source-id: 5cbe56e0d72d322f540bccffb60bcdbb15385ee8
