irc/polari: add missing USE_GNOME=libadwaita

Otherwise fails to run:

% polari

(polari:36417): Gjs-CRITICAL **: 16:32:52.548: JS ERROR: Error: Requiring Adw, version none: Typelib file for namespace 'Adw' (any version) not found
require@resource:///org/gnome/gjs/modules/esm/gi.js:16:28
@gi://Adw:3:25

• Message: 16:32:52.550: Execution of main.js threw exception: Module <main> threw an exception