Make tests pass after 2024

[bmwiedemann]

Background:
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 package build.

See https://reproducible-builds.org/ for why this matters.

I tested that this patch makes tests pass in 2037.

This is somewhat related to older PR #581

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what problem you are trying to solve with this PR?
• Have you added information on what your changes do and why you chose this as your solution?
• Have you written new tests for your changes?
• Does your submission pass tests?
• This project follows PEP8 style guide. Have you run your code against the 'flake8' linter?

[codecov]

Codecov Report

Merging #606 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #606      +/-   ##
==========================================
- Coverage    65.6%   65.58%   -0.03%     
==========================================
  Files         103      103              
  Lines       25614    25614              
==========================================
- Hits        16805    16799       -6     
- Misses       8809     8815       +6

Impacted Files	Coverage Δ
src/saml2/validate.py	73.33% <0%> (-2.75%)	⬇️
src/saml2/time_util.py	87.42% <0%> (+0.59%)	⬆️

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[bmwiedemann]

For some reason, this makes 8 tests fail on i586.
one failure message is about 2999-12-13T10:05:05Z not being a valid XML dateTime.

[c00kiemon5ter]

For some reason, this makes 8 tests fail on i586.
one failure message is about 2999-12-13T10:05:05Z not being a valid XML dateTime.

Is this python2? Can you check what import sys; print(sys.maxint) returns? I am guessing the system cannot represent the date as a number.