fix datavalidation errors on fluent theme.

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

@@ -35,7 +35,7 @@
       <ItemsControl Items="{Binding}">
         <ItemsControl.ItemTemplate>
           <DataTemplate>
-            <TextBlock Text="{Binding Message}" Foreground="{DynamicResource SystemControlErrorTextForegroundBrush}" TextWrapping="Wrap" />
+            <TextBlock Text="{Binding }" Foreground="{DynamicResource SystemControlErrorTextForegroundBrush}" TextWrapping="Wrap" />
           </DataTemplate>
         </ItemsControl.ItemTemplate>
       </ItemsControl>