screen-cast/window-stream: Mark as configured

This is needed for the pointer to be exposed to an existing libei session.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3403>

src/backends/meta-screen-cast-window-stream.c

@@ -99,6 +99,7 @@ meta_screen_cast_window_stream_new (MetaScreenCastSession     *session,
                          "cursor-mode", cursor_mode,
                          "flags", flags,
                          "window", window,
+                         "is-configured", TRUE,
                          NULL);
 }