Allow tests to pass after 2020

[bmwiedemann]

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While working on reproducible builds for openSUSE, I found that
our python-pysaml2 package failed to build because of its tests after 2020.

This change helps to verify reproducible builds - making sure that software builds produce the same results anywhere anytime.
See https://reproducible-builds.org/ for why this matters.

Note: There are some remaining issues with SSL certs expiring in 2025.

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[c00kiemon5ter]

Hello and thanks for looking into this.

While what you propose resolves your issue, it is not a real fix, in the sense that it moves the problem to another time-span. What will happen (in the exceptional! case that these tests are still in use) in 2998?

We've already fixed a similar problem (and should fix those the same way) by mocking the actual time the system thinks it operates at. I will prepare a fix soon.

[bmwiedemann]

I'm not at all worried about 2998 - neither of us will be around and probably not even this software.
And in the unlikely case, that someone is still running these tests then, they should be able to fix it.
We could even push the date to 9999 to give it more time than the pyramids in Egypt.