tests: update expired certificate
    
    This is a short term fix to un-break the unit tests. The proper fix
    would be to create the certificates at runtime during the tests.
    
    Related to https://pagure.io/SSSD/sssd/issue/3436
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    (cherry picked from commit 2ccfa9502abf52941d8b6e44b5f7cfdd13311a2d)
    (cherry picked from commit a3f85d196d14d2699af3ccd87c69c89287ce09fa)