Freeze break request for gnome-shell

[Florian Müllner <fmuellner gnome org>]

Hey everyone!

As you may know, we now have an official "Extensions" app for managing 
gnome-shell extensions. Unfortunately we missed adding appdata for it, 
so it doesn't show up in GNOME Software at all.

I would like to address this for 3.36.1 as part of 
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1081, but 
it adds a new translatable string for the description:

"GNOME Extensions handles updating extensions, configuring extension 
preferences and removing or disabling unwanted extensions."

That string has been heavily inspired by the release notes, so 
hopefully it doesn't impose too much work on translators.

Stay safe,
Florian