flake8 releases 5.0.1 today, and it raises the following issue:

ModuleNotFoundError: No module named 'flake8.plugins.manager'

see: https://github.com/Project-MONAI/model-zoo/runs/7603793727?check_suite_focus=true#step:7:83

I think we may need to fix the version to 4.0.1 so far, and adjust it later.