Python 3.12 creates these warnings:

.tox/py312/lib/python3.12/site-packages/dateutil/tz/tz.py:37
  /home/nicco/open-web-calendar/.tox/py312/lib/python3.12/site-packages/dateutil/tz/tz.py:37: DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).
    EPOCH = datetime.datetime.utcfromtimestamp(0)

test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[-2019-03-04 07:00-0]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[-2019-03-04 04:00-180]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[Etc/GMT 3-2019-03-04 04:00-180]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[Etc/GMT 5-2019-03-04 02:00-300]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[undefined-2019-03-04 06:00-60]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[undefined-2019-03-04 07:00-0]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[UTC-2019-03-04 07:00-180]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[Europe/London-2019-03-04 07:00--240]
test/test_special_timezones.py::test_that_timezones_do_not_create_an_error[Europe/Berlin-2019-03-04 08:00-0]
  /home/nicco/open-web-calendar/test/../convert_to_dhtmlx.py:114: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
    else datetime.datetime.utcnow()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

Please remove them.