Make tests pass after 2028

[bmwiedemann]

This PR was done while working on reproducible builds for openSUSE.

[jacobtomlinson]

Thanks for this. Seems sensible to bump these dates out.

Out of curiosity how does this change make builds reproducible?

[bmwiedemann]

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 +15 years, because that is how long I expect some software will be used in some places.
This showed up failing tests in our python-distributed package build.
See https://reproducible-builds.org/ for why this matters.

So in the end it is about getting identical build results anytime anywhere and expirations break the anytime part.

[jacobtomlinson]

Really interesting thanks!

CI failures appear to be related to #4404.