Bug#1079431: laby: please migrate from deprecated gtksourceview3 to gtksourceview4 (or 5)

[Simon McVittie <smcv@debian.org>]

Source: laby
Version: 0.7.0-2
Tags: trixie sid upstream
Control: block -1 by 1079417
Control: block 996689 by -1
User: pkg-gnome-maintainers@lists.alioth.debian.org
Usertags: oldlibs

gtksourceview3 was superseded in 2018 by gtksourceview4 (a new major
upstream release, but still using GTK 3). There's a porting guide here,
which is mostly "stop using deprecated APIs" plus a few function renames:
https://gnome.pages.gitlab.gnome.org/gtksourceview/gtksourceview5/porting-guide-3-to-4.html

gtksourceview3 is unmaintained and hasn't had an upstream release for more
than 5 years, so it would be great if the remaining gtksourceview3
applications can move to gtksourceview4 before trixie.

In the case of laby, switching to gtksourceview4 would presumably require
changes in lablgtk3 (#1079417).

Thanks,
    smcv