fix: Uno specific workaround for invalid assert in ComboBox

src/Uno.UI/UI/Xaml/Controls/ComboBox/ComboBox.partial.mux.cs

@@ -2447,7 +2447,9 @@ private void OnCharacterReceived(UIElement pSender, CharacterReceivedRoutedEvent
 			char keyCode;
 			keyCode = pArgs.Character;
 
-			if (!IsEditable)
+			// Uno specific: In WinUI this condition is only !IsEditable - however this seems to be wrong
+			// as the KeyDown handling also considers IsInSearchingMode.
+			if (!IsEditable && !IsInSearchingMode())
 			{
 				// Space should have been handled by now because we handle the Space key in the KeyDown event handler.
 				// NOTE: The 2 below specifies the map type, and maps VK to CHAR