gtk: Add missing gio_v2_80 feature

Required by the new gio::Application::version property

Author: bilelmoussaoui

gtk4/Cargo.toml

@@ -24,6 +24,7 @@ v4_8 = ["ffi/v4_8", "v4_6", "gdk/v4_8"]
 v4_10 = ["ffi/v4_10", "v4_8", "gdk/v4_10", "gsk/v4_10"]
 v4_12 = ["ffi/v4_12", "v4_10", "gdk/v4_12"]
 v4_14 = ["ffi/v4_14", "v4_12", "gsk/v4_14"]
+gio_v2_80 = ["gio/v2_80"]
 xml_validation = ["gtk4-macros/xml_validation"]
 blueprint = ["gtk4-macros/blueprint"]
 unsafe-assume-initialized = []