tests/mainwindow: disable part of test on OSX
tests/mainwindow: disable part of test on OSX

We can't create an Archive or Job, because it can't write its database, because
it doesn't have an app/app_data dir, because we don't have a config file set
yet, because we don't have TSettings yet.

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