Add Inhibit=none to sway-portals.conf

default=gtk is 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 will not
idle-inhibit when playing videos.

Adding org.freedesktop.impl.portal.Inhibit=none to sway-portals.conf
will cause at least Firefox to use wayland's idle-inhibit protocol
instead, which sway does implement.

Fixes #2

sway-portals.conf

@@ -2,3 +2,8 @@
 default=gtk
 org.freedesktop.impl.portal.ScreenCast=wlr
 org.freedesktop.impl.portal.Screenshot=wlr
+# xdg-desktop-portal-gtk's implementation uses org.gnome.SessionManager and
+# org.freedesktop.ScreenSaver, neither of which is implemented by Sway. This
+# will cause some programs (e.g. Firefox) to use Wayland's idle-inhibit
+# protocol instead, which sway does implement.
+org.freedesktop.impl.portal.Inhibit=none