audioDeviceSelection: Center-align icons

When the icon area gets allocated additional space, we want the
icons centered rather than left-aligned. This may happen in locales
with long-ish translations for the title or buttons when only a
subset of possible icons is shown.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3307

js/ui/audioDeviceSelection.js

@@ -43,6 +43,7 @@ var AudioDeviceSelectionDialog = GObject.registerClass({
 
         this._selectionBox = new St.BoxLayout({
             style_class: 'audio-selection-box',
+            x_align: Clutter.ActorAlign.CENTER,
             x_expand: true,
         });
         content.add_child(this._selectionBox);