requirements_dev.txt and tox.ini do not agree with each other

[matthiask]

Bit late to catch this here, but when I was trying to follow the contributing guide and use make test this was breaking on me as django-template-partials was only added to the tox config, and not to requirements_dev.txt as well

Originally posted by @TomHall2020 in #2117 (comment)

I also noticed that the requirements file still specifies django-csp<4.