Commit 2e26f39d switched to a new overload of KStartupInfo::setNewStartupId
which was introduced in KWindowSystem 5.65, but didn't increase the
required frameworks version, so trying to build with an older KF5 (in my
case 5.54) would pass CMake tests but fail with "error: no matching
function for call to 'KStartupInfo::setNewStartupId'".

If this version bump isn't acceptable, then feel free to revert this
*and* 2e26f39d :)