Nose is no longer maintained and is incompatible with Python 3.10, so
can no longer be used. This change runs `coverage` manually to collect
coverage and uses `pytest` to run doctests, collectively covering what
was tested using django_nose.
As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:
> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.
Test Plan: Manually visited all the links I’ve modified.
