extensions-app: Set app version

GApplication now has a `version` property to support a `--version`
flag on the commandline. It's a nice touch, so set it.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3216>

subprojects/extensions-app/js/main.js

@@ -14,7 +14,10 @@ var Application = GObject.registerClass(
 class Application extends Adw.Application {
     _init() {
         GLib.set_prgname('gnome-extensions-app');
-        super._init({application_id: Package.name});
+        super._init({
+            application_id: Package.name,
+            version: Package.version,
+        });
 
         this.connect('window-removed', (a, window) => window.run_dispose());
     }