Fails to build with gcc 14

Hey,

I just got a report on Debian that xfce4-notes-plugin fails to build with gcc-14 while it was building fine with gcc-13. Downstream bug is at https://bugs.debian.org/1075660 and the log is here:

application.c:3461:87: error: passing argument 2 of 'gtk_menu_shell_append' from incompatible pointer type [-Wincompatible-pointer-types]
 3461 |                                 gtk_menu_shell_append ((GtkMenuShell*) _data2_->menu, _tmp9_);
      |                                                                                       ^~~~~~
      |                                                                                       |
      |                                                                                       GtkMenuItem * {aka struct _GtkMenuItem *}
In file included from /usr/include/gtk-3.0/gtk/gtkmenu.h:33,
                 from /usr/include/gtk-3.0/gtk/gtklabel.h:34,
                 from /usr/include/gtk-3.0/gtk/gtkaccellabel.h:35,
                 from /usr/include/gtk-3.0/gtk/gtk.h:33:
/usr/include/gtk-3.0/gtk/gtkmenushell.h:92:55: note: expected 'GtkWidget *' {aka 'struct _GtkWidget *'} but argument is of type 'GtkMenuItem *' {aka 'struct _GtkMenuItem *'}
   92 |                                         GtkWidget    *child);
      |                                         ~~~~~~~~~~~~~~^~~~~
application.c:3470:63: error: passing argument 2 of 'gtk_menu_shell_append' from incompatible pointer type [-Wincompatible-pointer-types]
 3470 |         gtk_menu_shell_append ((GtkMenuShell*) _data2_->menu, (GtkMenuItem*) mi_sep);
      |                                                               ^~~~~~~~~~~~~~~~~~~~~
      |                                                               |
      |                                                               GtkMenuItem * {aka struct _GtkMenuItem *}

Unfortunately the C code actually derives from Vala code and I'm not yet able to track the original function. I'll investigate but I guess you know more about Vala than me :)