[libadwaita] Revert "demo: Use .toggle-group instead of .linked for flap toggles"

[Alexander Mikhaylenko <alexm src gnome org>]

commit 913630e72433e1c2fd834bbef048394cf78cfc71
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Mon Sep 13 11:08:44 2021 +0000

    Revert "demo: Use .toggle-group instead of .linked for flap toggles"
    
    This reverts commit fee4065f2041ebe59a61371ebe5a7c6d78b24e9f

 examples/adw-flap-demo-window.ui | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/examples/adw-flap-demo-window.ui b/examples/adw-flap-demo-window.ui
index 02e47713..720cb766 100644
--- a/examples/adw-flap-demo-window.ui
+++ b/examples/adw-flap-demo-window.ui
@@ -105,7 +105,7 @@
                                   <object class="GtkBox">
                                     <property name="valign">center</property>
                                     <style>
-                                      <class name="toggle-group"/>
+                                      <class name="linked"/>
                                     </style>
                                     <child>
                                       <object class="GtkToggleButton" id="start_toggle_button">