qt,tests: Allow 1-day-offset for expiration date

* lang/qt/tests/t-various.cpp (TestVarious::testSignKeyWithExpiration):
Assert that the expiration date is either 2106-02-05 or 2106-02-04.

This avoids a test failure if the test is run at 00:xx:xx in a location
that uses DST.

• GnuPG-bug-id: T5991