fix datetime without TZ warnings
here is a sample warning:
RuntimeWarning: DateTimeField Holiday.datetime_start received a naive datetime (2020-11-13 12:19:24.909491) while time zone support is active
Edited by Piotr Gawron
here is a sample warning:
RuntimeWarning: DateTimeField Holiday.datetime_start received a naive datetime (2020-11-13 12:19:24.909491) while time zone support is active