gradience: add glib-networking to buildInputs

The Gradience supports downloading community presets which are located
at GitHub using HTTPS:

https://github.com/GradienceTeam/Gradience/blob/af81166e2bca21b35948356753ea08ce5ba44ed0/gradience/backend/globals.py#L31-L34

However glib-networking is required for TLS support.

This patch adds this missing dependency to fix downloading Gradience
presets.

pkgs/applications/misc/gradience/default.nix

···
 , ninja
 , pkg-config
 , glib
+, glib-networking
 , desktop-file-utils
 , gettext
 , librsvg
···
   ];
 
   buildInputs = [
+    glib-networking
     libadwaita
     libportal
     libportal-gtk4