Update package metadata and tox for supported Python versions.

Review Request #11994 — Created Jan. 24, 2022 and submitted — Latest diff uploaded


Django Evolution


This updates the classifiers for the package to list Python 3.9 and 3.10
support, and to include metadata that will help ensure pip installs
the right package based on the current version of Python in the future,
which will matter as we end up dropping older versions down the road.

The tox configuration has also been updated to test Python 3.10, and to
use compatible release clauses for the right versions of Django.

Successfully built the package.

Tox successfully ran all unit tests.