introspection: Add missing annotation
introspection: Add missing annotation

https://bugzilla.gnome.org/show_bug.cgi?id=661716

saitoha/vte-sixel,asivokon/vte-fx,saitoha/vte-sixel,pjm0616/vte,jessevdk/vte,thestinger/vte-ng,saitoha/vte-sixel,jessevdk/vte,pjm0616/vte,jessevdk/vte,asivokon/vte-fx,thestinger/vte-ng,flaxandteal/gasket-vte,flaxandteal/gasket-vte,rvu95/vte,rvu95/vte,flaxandteal/gasket-vte,asivokon/vte-fx,thestinger/vte-ng,rvu95/vte,pjm0616/vte,rvu95/vte,asivokon/vte-fx,jessevdk/vte,flaxandteal/gasket-vte