x11-toolkits/gtkmm40: update to 4.20.0
Update to 4.20.0
4.20.0 (stable) 2025-09-19 Gdk: * PixbufAnimation, PixbufAnimationIter: Deprecate these classes. GdkPixbufAnimation and GdkPixbufAnimationIter are deprecated since gdk-pixbuf 2.44. * PixbufLoader: Deprecate get_animation(). (Kjell Ahlstedt)
PR: 292077