Future Dev - resolve TimeZone aware

[rstan-dev]

Address timezone warnings - warnings.warn("DateTimeField %s received a naive datetime (%s)

not sure where these warnings are only showing up in the test

System check identified no issues (0 silenced).
/workspace/.pip-modules/lib/python3.8/site-packages/django/db/models/fields/init.py:1416: RuntimeWarning: DateTimeField Van.date_added received a naive datetime (2024-01-02 12:00:00) while time zone support is active.
warnings.warn("DateTimeField %s received a naive datetime (%s)"

./workspace/.pip-modules/lib/python3.8/site-packages/django/db/models/fields/init.py:1416: RuntimeWarning: DateTimeField Van.date_added received a naive datetime (2024-01-02 12:00:00) while time zone support is active.
warnings.warn("DateTimeField %s received a naive datetime (%s)"

.............../workspace/.pip-modules/lib/python3.8/site-packages/django/db/models/fields/init.py:1416: RuntimeWarning: DateTimeField Van.date_added received a naive datetime (2024-03-02 12:00:00) while time zone support is active.
warnings.warn("DateTimeField %s received a naive datetime (%s)"

/workspace/.pip-modules/lib/python3.8/site-packages/django/db/models/fields/init.py:1416: RuntimeWarning: DateTimeField Van.date_added received a naive datetime (2024-02-02 12:00:00) while time zone support is active.
warnings.warn("DateTimeField %s received a naive datetime (%s)"
...........