Lint session fails following tests-3.x session runs

[DrGFreeman]

Describe the bug
In the nox repository, when running the lint session after having run one of the tests-3.x sessions, flake8 fails on analysis of the test generated virtual environments in tests/resources/.nox/:

nox > flake8 nox tests noxfile.py setup.py
... (lines skipped)
tests/resources/.nox/test-arg-datetime-datetime-1980-1-1-0-0/lib/python3.9/site-packages/wheel/bdist_wheel.py:140:72: W504 line break after binary operator
nox > Command flake8 nox tests noxfile.py setup.py failed with exit code 1
nox > Session lint failed.

How to reproduce

Run nox -s tests-3.8 lint

Expected behavior

The lint session passes without errors.

Notes

• This can be fixed by adding exclude = .nox in the .flake8 file.
• This is not detected in CI since the lint job runs in isolation from the test jobs.

[cjolowicz]

Thank you for catching and reporting this @DrGFreeman :)

#445 avoids creating a .nox directory under tests in the first place. That should fix this issue.