gtk4: updated to 4.12.1

Overview of Changes in 4.12.1, 25-08-2023
=========================================

* GtkGridView:
- Fix a crash when scrolling

* GtkColumnView:
- Fix a refcounting issue in the new scroll_to api

* GtkTreeView
- Fix style classes for sort arrows

* GtkEntry:
- Improve tracking of user changes (for undo)

* GtkNotebook:
- Fix a critical when switching pages

* GtkColor/FontDialogButton:
- Make these widgets activatable

* GtkMenuButton:
- Fix problems with focus handling
- Fix problems with DND

* Printing
- Fix the cpdb backend build

* MacOS:
- Make file filters work again

* GSK:
- Fix issues with color matrix nodes

* Wayland:
- Fix a crash with compositors other than gnome-shell

* Translation updates:
Polish
Swedish

(adam)