mainwindow.cpp fix "bitwise operation between different enumeration types"

/home/n/kde/src/utilities/yakuake/app/mainwindow.cpp:397:74: warning: bitwise operation between different enumeration types ‘Qt::Modifier’ and ‘Qt::Key’ is deprecated [-Wdeprecated-enum-enum-conversion] 397 | actionCollection()->setDefaultShortcut(action, QKeySequence(Qt::CTRL | Qt::Key_Tab));