nix: test direct_wayland behaviour

This should never be used outside tests unless you absolutely know what you're doing or are using GNOME.

Signed-off-by: Ophestra <cat@gensokyo.uk>

nixos.nix

@@ -118,6 +118,7 @@ in
                         };
                         map_real_uid = app.mapRealUid;
                         no_new_session = app.tty;
+                        direct_wayland = app.insecureWayland;
                         filesystem =
                           let
                             bind = src: { inherit src; };