Replace pytest-pep8

[1313e]

Starting in pytest v6.0.0, pytest-pep8 is no longer supported as it uses a plugin structure that pytest has deprecated (this is why tests are currently failing).
Given that the pytest-pep8 plugin has not been updated for over 5 years now, it is doubtful that it will be updated for this.

I will either have to remove PEP8-compliancy testing (which I would like to avoid) or replace the plugin with one that does the same thing (I however do not know of one that does that as well).
I could also fix the problem myself by migrating the package from BitBucket to GitHub, and fixing the problem.

Anyone has any ideas for alternative pytest plugins or methods that perform PEP8 testing?

[graingert]

@1313e pytest-flake8, although it's recommended to run flake8 in tox/pre-commit rather than pytest