`portals.conf` uses the gtk backend for Inhibit, which does not work

Description:

Arch ships a sway-portals.conf, which has default=gtk. This default is also used for org.freedesktop.impl.portal.Inhibit. However, xdg-desktop-portal-gtk's implementation of this interface tries to use the DBus interfaces org.gnome.SessionManager and org.freedesktop.ScreenSaver, neither of which is implemented by Sway.

One way this manifests is that newer versions of Firefox (I'm running firefox-developer-edition 122.0b4-1, sway 1:1.8.1-4, swayidle 1.8.0-1) will not idle-inhibit when playing videos.

The proposed fix for this is to add org.freedesktop.impl.portal.Inhibit=none to sway-portals.conf. This will cause at least Firefox to use wayland's idle-inhibit protocol instead, which sway does implement.