Core: fix deprecation warning in for utcnow()

[Berserker66]

What is this fixing or adding?

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). self.buildtime = datetime.datetime.utcnow()

How was this tested?

running setup.py build_exe on py 3.12

If this makes graphical changes, please attach screenshots.

[nicholassaylor]

LGTM, this should work now that 3.8 is binned

[black-sliver]

>>> from datetime import datetime, timezone
>>> datetime.utcnow().hour == datetime.now(timezone.utc).hour
True