python/mobility: UNIX <-> ETSI time conversion broken when local timezone is not UTC

What:

When the lcoal timezone is not UTC, conversion between UNIX and ETSI time and back, is broken.

For eaxmple, assuming Europe/Paris (CEST, GMT+0200) as the local timezone:

>>> from iot3.mobility.etsi import ETSI
>>> unix_now = time.time()
>>> etsi_now = ETSI.unix2etsi_time(unix_now)
>>> new_now = ETSI.etsi2unix_time(etsi_now)
>>> print(new_now - unix_now)
14399.999512434006

The delta is (almopst exactly) 4 hours, which is twixe the offset to GMT.

Expected:

The conversion properly handles the local timezone.

Most proobably, the culprit is commit a707109a49e2eb01e9bd923dfc9fd495c3ca2622 (python/iot3/mobility: compliance with python 3.12), which improperly converts from a timezone-aware to a naive datetime object.