Extend test cert to 2049-05-27

Extend test cert to 2049-05-27 instead of expiring in 2024-02-29

This update did not trigger y2038 bugs on 32-bit systems.

Without this patch, one test fails after 2024:
 doit:124: rsa pss key: gnutls_x509_crt_verify_data2                    |
 FAIL x509sign-verify (exit status: 1)

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.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated / NEWS entry present (for non-trivial changes)
• CI timeout is 2h or higher (see Settings/CICD/General pipelines/Timeout)

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code

Note: I used certtool -u to create the new cert, but am unsure why it is 2 lines shorter than the old one. Edit: using a newer version of certtool with --sign-params=RSA-PSS --key-type rsa-pss --salt-size=32 helped.