[bug#50850] [core-updates-frozen] Update to GNOME 40.

[Mathieu Othacehe <othacehe@gnu.org>]

Hello,

While fixing the GNOME packages build on the core-updates-frozen branch,
I noticed that some of them were really outdated.

Based on Raghav's work on the wip-gnome branch, there is a now a
wip-gnome40[1] branch that performs a full upgrade to GNOME 40. I also
fixed some of the GNOME integration issues we had:

- Added gnome-photos and gnome-music to the meta gnome package.
- Fixed gnome-weather integration[2].
- Fixed gnome-music start[3].
- Fixed gnome-todo build[4].

This branch can be tested this way:

--8<---------------cut here---------------start------------->8---
./pre-inst-env guix system vm gnu/system/examples/desktop.tmpl 
--8<---------------cut here---------------end--------------->8---

Given that the changes are almost restricted to the gnome.scm file, I
think that we can reasonably merge it inside the core-updates-frozen
branch soon.

Thanks,

Mathieu

[1]: https://git.savannah.gnu.org/cgit/guix.git/log/?h=wip-gnome40
[2]: https://issues.guix.gnu.org/39324
[3]: https://issues.guix.gnu.org/49063
[4]: https://issues.guix.gnu.org/40410