setuptools appends --find-links to pip if dependency_links is found, and
both takes URLs [1][2].

[1] https://github.com/pypa/setuptools/blob/v51.0.0/docs/userguide/dependency_management.rst#dependencies-that-arent-in-pypi
[2] https://pip.pypa.io/en/stable/reference/pip_install/#cmdoption-f