Fix StyleIncludeTests.

Wasn't finding `RelativeSource` type at times.

src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github

@@ -1 +1 @@
-Subproject commit 5e498f8bcca403a34aff5efc825cbb4e12b7fa8e
+Subproject commit 491de981dd4433ee58bc9540e2cd4a5d168f8168

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/StyleIncludeTests.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Controls;
+using Avalonia.Data;
 using Avalonia.Markup.Xaml.Styling;
 using Avalonia.Markup.Xaml.XamlIl.Runtime;
 using Avalonia.Media;
@@ -15,6 +16,11 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml;
 
 public class StyleIncludeTests
 {
+    public StyleIncludeTests()
+    {
+        System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(typeof(RelativeSource).TypeHandle);
+    }
+
     [Fact]
     public void StyleInclude_Is_Built()
     {