Implementing it in the overrides as PyGObject won't be able to properly
convert python values to GValues in some cases. Using
g_object_set_property works as some logic is implemented inside
PyGObject for that particular case. This is a "regression" due
to https://bugzilla.gnome.org/review?bug=769789&attachment=348766 were
we end up with an OverflowError while setting G_TYPE_UINT children
properties.
