GNOME 3 screenshot for gnu.org

[Amin Bandali]

Hello Guix,

The FSF is looking to refresh the screenshot on www.gnu.org, and
add new ones showcasing Mate and GNOME 3.  I suggested taking the
GNOME 3 screenshot from GuixSD.

I see there's already a GNOME 3 screenshot [0] on the Guix page.
Given that the screenshot seems to be from 2016, would you like
to take a new one, or is it fine if we use the current one?

[0]: https://www.gnu.org/software/guix/screenshots/gnome/

-amin