build: bump development version
build: bump development version

This should have been done when branching for 4.6. There is no anticipation
of a 4.8 release (as instead we'll be movin to GTK 4). But this at least
keeps build scripts working which are requiring >= 4.6.

GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview