Describe the bug

Adding --no-reuse-existing-virtualenvs does not seem to ignore the cache, and instead just reuses the existing environments anyway. Happened on the previous version, and then did a brew upgrade, and 2021.10.1 also has this problem. Unless I misunderstand this option, pretty sure it's broken.

How to reproduce

@nox.session(reuse_venv=True)
def type(session):
    session.install('mypy')
    session.run('mypy')

(simplified slightly, should be unimportant)

$ nox --no-reuse-existing-virtualenvs -s type
nox > Running session type
nox > Re-using existing virtual environment at .nox/type.

Expected behavior
The existing virtual environment should not have been reused. (It really was, not just visually; I was trying to remove an item from the install list, but it remained installed).