xdg-shell: Bump unstable version

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/clients/window.c b/clients/window.c
index 57f7a8d..a04cef9 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -5245,7 +5245,7 @@
 	xdg_shell_ping,
 };
 
-#define XDG_VERSION 4 /* The version of xdg-shell that we implement */
+#define XDG_VERSION 5 /* The version of xdg-shell that we implement */
 #ifdef static_assert
 static_assert(XDG_VERSION == XDG_SHELL_VERSION_CURRENT,
 	      "Interface version doesn't match implementation version");