chore: Add pytz as a dependency for tests

[abhiabhi94]

• since django 4.0, pytz is no longer a dependency, but is still required
  for rest framework.

[codecov-commenter]

Codecov Report

Merging #234 (8972995) into develop (066c732) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #234   +/-   ##
========================================
  Coverage    99.89%   99.89%           
========================================
  Files           55       55           
  Lines         1969     1969           
  Branches       158      158           
========================================
  Hits          1967     1967           
  Misses           1        1           
  Partials         1        1           

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