More refactoring ULS font selection tests

Change-Id: I6595e279657948265c45407be2c01a4587fdbc94

tests/browser/features/support/pages/panel_page.rb

@@ -31,6 +31,8 @@ class PanelPage
 	span(:trigger_cog, class: 'uls-settings-trigger')
 	a(:trigger_personal, class: 'uls-trigger')
 
+	select(:selected_content_font, id: 'content-font-selector')
+
 	select(:select_font_for_interface, id: 'ui-font-selector')
 	select(:select_font_for_content, id: 'content-font-selector')