pycodestyle-2.4.0 added new warnings W605 and W606, which needs to be
addressed or future versions of python3 will refuse to run.
(OpenStack CI's flake8 is pre pycodestyle age, flake8 version isn't
managed by g-r, but that's another story. No release of flake8
supports pycodestyle 2.4.0 yet. ;)
nova seems to have ~200 of those warnings, while other projects don't
have much, FWIW.
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