[DOCS] Dealing with old numpy dependencies

[matteobachetti]

Hi, I'm trying to add tests of very old versions of our code at https://stingray.science/stingray-benchmarks/

Old versions depend on old Astropy and numpy versions, which have evolved considerably and, in turn, have their needs. Now, I'm getting an error which ends with

    < ModuleNotFoundError: No module named 'setuptools'

This does not change if, in my setup, I include setuptools among the dependencies of this environment:

    {"python": "3.8", "req": {"pip": "20.3.3", "numpy": "<1.20", "setuptools": "50", "astropy": "<5.0"}},

Are there any guidelines specifically for dealing with very old packages? Thanks in advance!

[HaoZeke]

Sorry for the late reply, is this a problem with all the backends? (mamba / conda/virtualenv)?