Bump ATK dependency to 2.12
Bump ATK dependency to 2.12

... for the new AtkValue interface that we implement.

Sidnioulz/SandboxGtk,jessevdk/gtk,chergert/gtk,Sidnioulz/SandboxGtk,chergert/gtk,davidgumberg/gtk,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,ahodesuka/gtk,jigpu/gtk,jessevdk/gtk,davidgumberg/gtk,Adamovskiy/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,chergert/gtk,Adamovskiy/gtk,jadahl/gtk,jadahl/gtk,Adamovskiy/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,davidgumberg/gtk,ahodesuka/gtk,chergert/gtk,jigpu/gtk,jadahl/gtk,Adamovskiy/gtk,Sidnioulz/SandboxGtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,alexlarsson/gtk,Lyude/gtk-,chergert/gtk,Adamovskiy/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,chergert/gtk,davidgumberg/gtk,grubersjoe/adwaita,jigpu/gtk,grubersjoe/adwaita,ahodesuka/gtk,ahodesuka/gtk,alexlarsson/gtk,jessevdk/gtk,ahodesuka/gtk,grubersjoe/adwaita,jadahl/gtk,jigpu/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,chergert/gtk,davidgumberg/gtk,jigpu/gtk,Lyude/gtk-,davidgumberg/gtk,Lyude/gtk-,jigpu/gtk,Adamovskiy/gtk,davidgumberg/gtk,Lyude/gtk-,chergert/gtk,jessevdk/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,Lyude/gtk-,ahodesuka/gtk,jadahl/gtk,grubersjoe/adwaita,jessevdk/gtk,jessevdk/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jessevdk/gtk,alexlarsson/gtk,jigpu/gtk,Lyude/gtk-