tests/translations: use QApplication::setOrganizationName()
tests/translations: use QApplication::setOrganizationName()

We need QApplication for QTEST_MAIN, since the .pro file includes
    QT = gui widgets

There's no point using the base class QCoreApplication::setOrganizationName(),
as that just means that we'd need the <QCoreApplication> header.

Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui