If you have the /etc/timezone file set to a timezone string, pendulum.UTC has that timezone's utcoffset instead of None

[x] I am on the latest Pendulum version.
[x] I have searched the issues of this repo and believe that this is not a duplicate.

OS version and name: linux docker container (python3.10-slim) running on a mac
Pendulum version: 3.0.0

Issue

This appears to be a bug in ZoneInfo that moved into pendulum in the 3.0 release now that TimeZone subclasses ZoneInfo.

Simple repro:

In a Docker container:

FROM python:3.10-slim

RUN pip install pendulum

RUN echo "Asia/Shanghai" > /etc/timezone

Then in Python:

import pendulum, datetime
pendulum.UTC.utcoffset(datetime.datetime(2024, 3, 12, 0, 0, 0, 0)))

outputs datetime.timedelta(seconds=28800) (the utcoffset of the timezone in /etc/timezone) instead of the expected None return value for UTC.

This breaks all kinds of things.

The same issue happens with a ZoneInfo object:

datetime.timedelta(seconds=28800)