Revert commit e454314daa (NinjaMultiConfig: Update tests for the new
dependency change, 2023-07-05, v3.28.0-rc1~96^2) because we are about
to revert the change for which it updated tests.
The minimum CMake version for Qt6 is 3.16, so all the calls to
cmake_minimum_required() are updated here to enforce that
minimum. This will avoid any CMake version-related warnings
from Qt.
Avoid hard-coding Qt5 where the tests could now be using
Qt5 or Qt6.
Fixes: #22188
Orkun Tokdemir