Add unit tests for recently introduced regressions

[matteius]

This ticket is to add tests for some of the recent regressions and feature changes:

• pipenv run pip freeze should have predictable and clean stdout logging
• pipenv run script --quiet should still load .env vars (and not log the message about it)
• Bonus would be: a test for the package index restriction. This might be hard because we only have a single pypi server running, but I was thinking about an example that relies on pulling from our named pypi server when pypi.org is avialable and a newer package version exists there, so that might be a feasible test to add.

[matteius]

Fixed with: #5017