assignments from incompatible pointer types

Compiling with GCC 15 I get

 * QA Notice: Package triggers severe warnings which indicate that it
 *            may exhibit random runtime failures.
 * src/timeshift.p/Utility/GtkHelper.c:359:17: warning: assignment to ‘GtkBox *’ {aka ‘struct _GtkBox *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift.p/Utility/Gtk/CustomMessageDialog.c:247:16: warning: assignment to ‘GtkBox *’ {aka ‘struct _GtkBox *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift.p/Utility/Gtk/TerminalWindow.c:431:16: warning: assignment to ‘GtkContainer *’ {aka ‘struct _GtkContainer *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Utility/GtkHelper.c:359:17: warning: assignment to ‘GtkBox *’ {aka ‘struct _GtkBox *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Utility/Gtk/CustomMessageDialog.c:247:16: warning: assignment to ‘GtkBox *’ {aka ‘struct _GtkBox *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Utility/Gtk/TerminalWindow.c:431:16: warning: assignment to ‘GtkContainer *’ {aka ‘struct _GtkContainer *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/BackupDeviceBox.c:1587:16: warning: assignment to ‘GtkContainer *’ {aka ‘struct _GtkContainer *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/ExcludeMessageWindow.c:519:16: warning: assignment to ‘GtkBox *’ {aka ‘struct _GtkBox *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/ExcludeMessageWindow.c:666:17: warning: assignment to ‘GtkBox *’ {aka ‘struct _GtkBox *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/RestoreDeviceBox.c:1812:16: warning: assignment to ‘GtkContainer *’ {aka ‘struct _GtkContainer *’} from incompatible pointer type ‘GtkWidget *’ {aka ‘struct _GtkWidget *’} [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/MainWindow.c:1753:64: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/MainWindow.c:1762:56: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/SnapshotListBox.c:1661:56: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/SnapshotListBox.c:1679:57: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/SnapshotListBox.c:1697:57: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/SnapshotListBox.c:1715:57: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]
 * src/timeshift-gtk.p/Gtk/SnapshotListBox.c:1733:57: warning: passing argument 2 of ‘gtk_menu_shell_append’ from incompatible pointer type [-Wincompatible-pointer-types]

I am not quite sure if this really is a problem of timeshift or if vala is the culprit here, generating that code as I can not find it in the sources.

Reproduce the GCC 15 build and inspect the generated C locations listed under src/timeshift.p and src/timeshift-gtk.p, then trace each warning back to its Vala source. Compare the affected GTK assignments and gtk_menu_shell_append calls; done means the build no longer reports these incompatible-pointer warnings.