Make some fixes to the `coverage` Nox session
Make some fixes to the `coverage` Nox session

- Simplify it, by replacing a run with a Python if statement.
- Pass an env argument to the coverage call to ensure it will work.
sbidoul/pip,sbidoul/pip,pfmoore/pip,pradyunsg/pip,pypa/pip,pradyunsg/pip,pypa/pip,pfmoore/pip