fixed missing orientation on target

samples/SingleProjectSandbox/Properties/launchSettings.json

@@ -0,0 +1,12 @@
+{
+  "profiles": {
+    "SingleProjectSandbox": {
+      "commandName": "Project",
+      "launchBrowser": true,
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      },
+      "applicationUrl": "https://localhost:58713;http://localhost:58714"
+    }
+  }
+}

tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs

@@ -1438,7 +1438,10 @@ namespace Avalonia.Controls.UnitTests
             Orientation orientation = Orientation.Vertical)
                 where T : ItemsControl, new()
         {
-            var target = new VirtualizingStackPanel();
+            var target = new VirtualizingStackPanel
+            {
+                Orientation = orientation,
+            };
 
             items ??= new ObservableCollection<string>(Enumerable.Range(0, 100).Select(x => $"Item {x}"));