CI upgrade

[jaymedina]

Following the work on PR #56

@falkben has a couple suggestions on how the GitHub Actions workflow can be improved for astrocut:

• cutting out 3.6
• including 3.9 and 3.10
• updating the other dependencies we test against (e.g. which version of astropy and numpy)
• cleaning up the tox.ini file for anything we're not using, which i'm not even sure what we're not using at this point and what we are using.
• seeing why "Python 3.7 with dev version of key dependencies" ALWAYS fails (i know we mark is allowed failure... but if it always fails, it's not useful either)
• fixing python 3.8 windows 32 test

[pllim]

astropy 5.x has dropped Python 3.7. So if you are trying to install astropy dev in Python 3.7, it is going to always fail. I recommend you bump dev job to Python 3.10.

[ceb8]

@pllim That makes sense, it was around when 5.0 came out that that failure started, I just never got the time to figure out why it was breaking.