Fix PlacesItemModelTest, 2nd try

This partly reverts 15a5189b

The KDE CI does not have KDE_FULL_SESSION set, which means that KIO
doesn't add the recentlyused:// urls to the model, but defaults to the
old timeline:// urls instead.

In both cases KIO adds 2 places, so it is safe to always assume that the
expected model count is 14.