prefs: Replace 'content' list style

It's deprecated in favor of 'boxed-list'.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/213>

extensions/auto-move-windows/prefs.js

@@ -21,7 +21,7 @@ class AutoMoveSettingsWidget extends Adw.PreferencesGroup {
 
         this._list = new Gtk.ListBox({
             selection_mode: Gtk.SelectionMode.NONE,
-            css_classes: ['content'],
+            css_classes: ['boxed-list'],
         });
         this.add(this._list);
 

extensions/workspace-indicator/prefs.js

@@ -20,7 +20,7 @@ class WorkspaceSettingsWidget extends Adw.PreferencesGroup {
 
         this._list = new Gtk.ListBox({
             selection_mode: Gtk.SelectionMode.NONE,
-            css_classes: ['content'],
+            css_classes: ['boxed-list'],
         });
         this._list.connect('row-activated', (l, row) => row.edit());
         this.add(this._list);