test_timezone_creation_with_arbitrary_dates fails at some times

Describe the bug
When running tests at certain times in the future, test_timezone_creation_with_arbitrary_dates fails.

If applicable: Stack Trace

FTBFS-log.txt

To Reproduce
Steps to reproduce the behavior:
on Debian or openSUSE do

osc checkout openSUSE:Factory/python-khal && cd $_
osc build --vm-type=kvm --noservice --clean --build-opt=--vm-custom-opt="-rtc base=2037-09-04T00:00:00" standard

Expected behavior
Tests should continue to success reliably.

OS, version, khal version and how you installed it:

• The output of khal --version: 0.11.3
• Installation method: rpm
• python version: 3.10
• OS: openSUSE-Tumbleweed 20240329

Additional context

As part of my work on reproducible builds for openSUSE, I check that software still gives identical build results in the future.
The usual offset is +16 years, because that is how long I expect some software will be used in some places.
This showed up failing tests in our package build.
See https://reproducible-builds.org/ for why this matters.

Start by running the named test, test_timezone_creation_with_arbitrary_dates, using the reported future clock setting from the reproduction steps. Inspect the attached FTBFS-log.txt for the failure details and determine what makes the test fail in 2037. Done means the test passes reliably at the reported future date as well as under normal time.