fix flake8 lint (#18835)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18835
ghimport-source-id: 7b1f433ae51232822704d62699233688072cbc23
Stack from [ghstack](https://github.com/ezyang/ghstack):
* **#18835 fix flake8 lint**
* #18826 [jit] run cpp tests for non-cuda builds in test_jit.py
...again
Reviewed By: ZolotukhinM
Differential Revision: D14766790
fbshipit-source-id: 29361a407589092831dfbc3c5d63d2834934cd02
