data: disable Inhibit D-BUS interface in xdg-portals configuration (#2205)

data: disable Inhibit D-BUS interface in xdg-portals configuration (#2205)

The GTK xdg-portal implementation, which is used as
the default behind the wlr xdg-portal implementation,
exposes the Inhibit interface even on a non-Gnome
session. Unfortunately this D-BUS interface does not
work on labwc.
By explicitly disabling this interface, firefox and may be
other applications are not tricked into using the
xdg-portal interface but use the Wayland IdleInhibit
protocol instead which labwc supports.