fix: warning on Python 3.12 about deprecated utcfromtimestamp

[henryiii]

See https://docs.python.org/3.12/library/datetime.html#datetime.datetime.utcfromtimestamp

Subject: fix a warning when running on Python 3.12's betas.

Feature or Bugfix

• Bugfix

Purpose

• fix a warning when running on Python 3.12's betas.

Should be backward compatible (3.12's suggestion to use datetime.UTC was added in 3.11, so isn't that helpful - but that's just an alias for datetime.timezone.utc)

[henryiii]

Ahh, this used from datetime import datetime. 😮‍💨

[AA-Turner]

Thanks @henryiii!

A