KWindowSystem::forceActiveWindow -> KWindowSystem::activateWindow
Fix build error "libkcups/KCupsPasswordDialog.cpp:52:20: error: ‘forceActiveWindow’ is not a member of ‘KWindowSystem’".
Fix build error "libkcups/KCupsPasswordDialog.cpp:52:20: error: ‘forceActiveWindow’ is not a member of ‘KWindowSystem’".