Fix malformed XAML

samples/RenderTest/SideBar.xaml

@@ -1,4 +1,4 @@
-<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">>
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
   <Style Selector="TabControl.sidebar">
     <Setter Property="Template">
       <ControlTemplate>