test: add headless test for canselect handling.

tests/HeadlessTest.Ursa/Controls/NavMenuTests/CanSelectTests/TestView1.axaml.cs

@@ -0,0 +1,23 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+using Ursa.Controls;
+
+namespace HeadlessTest.Ursa.Controls.NavMenuTests.CanSelectTests;
+
+public partial class TestView1 : UserControl
+{
+    public TestView1()
+    {
+        InitializeComponent();
+    }
+
+    private void Menu_OnSelectionChanging(object? sender, SelectionChangingEventArgs e)
+    {
+        var newItem = e.NewItems;
+        if (newItem is [NavMenuItem { Name: "MenuItem2" }])
+        {
+            e.CanSelect = false; // Prevent selection change for MenuItem2
+        }
+    }
+}