feat:

1. fix #427.
2. add headless test for this fix.

tests/HeadlessTest.Ursa/App.axaml.cs

@@ -0,0 +1,13 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace HeadlessTest.Ursa;
+
+public partial class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+}