talos: fix Firefox inhibit behavior

See https://github.com/flatpak/xdg-desktop-portal-gtk/issues/465 for
details about the issue.

TL;DR: x-d-p-gtk doesn't report a failure to handle the idle inhibit to
Firefox, so Firefox doesn't fallback to the Wayland protocol.

hosts/talos/default.nix

@@ -173,6 +173,7 @@
   # home
   xdg.portal.config.sway = {
     "org.freedesktop.impl.portal.Settings" = "darkman";
+    "org.freedesktop.impl.portal.Inhibit" = "none";
   };
 
   # Copy the NixOS configuration file and link it from the resulting system