Error when checking whether to notify users

[djperrefort]

The should_notify_upcoming_expiration function is running into a type comparison error when notifying users.

Error notifying user "USER" on upcoming expiration of request 12345: can't compare datetime.datetime to datetime.date
Traceback (most recent call last):
  File "/home/keystone/.local/share/pipx/venvs/keystone-api/lib/python3.11/site-packages/keystone_api/apps/allocations/tasks/notifications.py", line 84, in notify_upcoming_expirations
    if should_notify_upcoming_expiration(user, request):
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/home/keystone/.local/share/pipx/venvs/keystone-api/lib/python3.11/site-packages/keystone_api/apps/allocations/tasks/notifications.py", line 54, in should_notify_upcoming_expiration
    if user.date_joined >= date.today() - timedelta(days=next_threshold):
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    TypeError: can't compare datetime.datetime to datetime.date