Migrate from pytz to zoneinfo

[jennifer-richards]

Description

As of Django 4.0, zoneinfo replaces pytz as Django's default timezone library. At Django 5.0, pytz support will be removed. In the effort to migrate Datatracker to Django 4 we have made use of the USE_DEPRECATED_PYTZ setting and the pytz_deprecation_shim package. Before we get to Django 5.0, we need to replace pytz entirely in the code base.

Code of Conduct

• I agree to follow the IETF's Code of Conduct

[jennifer-richards]

See https://pytz-deprecation-shim.readthedocs.io/en/latest/migration.html for suggestions on how to make the transition. Much of it will be little more than glorified search and replace.