Update MATE to 1.24

[Jonathan Brielmaier]

Hi folks,

as the next release is approaching fast, I thought it would be nice to
have MATE 1.24 in. Compared to other desktop environments (hi GNOME)
updating is straight forward.

I tested MATE 1.24 in a VM. There are two problems:
* MATE suffers from https://issues.guix.gnu.org/issue/38135, so you
can't start any applications from the menu. This is a MAJOR usability
bug. The fix for it is in core-updates.
* atril requires a newer glib/gio (also in core-updates).

I have two branches:
https://gitlab.com/jonsger/Guix/-/tree/wip-mate-1.24 based on master
https://gitlab.com/jonsger/Guix/-/tree/wip-mate-1.24-co based on
core-updates

I tried a VM on core-updates, but there are no substitutes. So I can't
really built it on my laptop.

So I guess we need a core-updates merge before a release, if we wanna
have MATE in a "release able" state.

~Jonathan