chore: Python 3.12 is the floor (NAPALM/driver-standard#6)

netOrk runs every driver in its own containers on Python 3.12, so 3.10
and 3.11 are no longer supported or tested. requires-python, mypy and
ruff move to 3.12, along with what ruff's pyupgrade rules then rewrite.

napalm_redfish/driver.py

@@ -26,7 +26,7 @@ member of ``Managers``/``Chassis`` when the links are missing).
 from __future__ import annotations
 
 import logging
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from typing import Any
 
 from napalm.base.exceptions import ConnectionException
@@ -123,7 +123,7 @@ def _timestamp(created: str | None) -> float | None:
     except ValueError:
         return None
     if when.tzinfo is None:
-        when = when.replace(tzinfo=timezone.utc)
+        when = when.replace(tzinfo=UTC)
     return when.timestamp()