Fix AutoCompleteBox

src/Avalonia.Themes.Fluent/Controls/AutoCompleteBox.xaml

@@ -1,17 +1,20 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:generic="using:System.Collections.Generic">
   <Design.PreviewWith>
     <Border Padding="20">
       <AutoCompleteBox Width="200">
         <AutoCompleteBox.ItemsSource>
-          Alabama
-          Alaska
-          Arizona
-          Arkansas
-          California
-          Colorado
-          Connecticut
-          Delaware
+          <generic:List x:TypeArguments="x:String">
+            Alabama
+            Alaska
+            Arizona
+            Arkansas
+            California
+            Colorado
+            Connecticut
+            Delaware
+          </generic:List>
         </AutoCompleteBox.ItemsSource>
       </AutoCompleteBox>
     </Border>