fix: add test time versioned dependency to flake8
fix: add test time versioned dependency to flake8

Add test time versioned dependency to flake8 to avoid the following
error during tests with python 3.x.

  flake8.exceptions.FailedToLoadPlugin: Flake8 failed to load plugin
  "pycodestyle.break_around_binary_operator" due to module 'pycodestyle'
  has no attribute 'break_around_binary_operator'.

ssato/python-anyconfig,ssato/python-anyconfig