Update django support

[hramezani]

Problem

• Remove Django 3.1 from Python 3.10 env in tox.

• Confirm support for Django 4.0

• Add USE_TZ setting.

Solution

Explain the solution that has been implemented, and what has been changed.

Commandments

• Write PEP8 compliant code.
• Cover it with tests.
• Update CHANGES.rst file to describe the changes, and quote according issue with GH-<issue_number>.
• Pay attention to backward compatibility, or if it breaks it, explain why.
• Update documentation (if relevant).

[codecov]

Codecov Report

Merging #513 (f39dd55) into master (fc5f8ad) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #513   +/-   ##
=======================================
  Coverage   95.15%   95.15%           
=======================================
  Files           6        6           
  Lines         825      825           
=======================================
  Hits          785      785           
  Misses         40       40           

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[hramezani]

Thanks @adamchainz for your review!

[MRigal]

LGTM! Good that we had no test or setup depending on pytz. Thanks @hramezani !