UIElement.Focus(FocusState.Programmatic); Returns true despite TextBox not losing focus

Nobody has claimed this yet.

### Describe the bug

```
private void TaskItemName_Enter(Microsoft.UI.Xaml.Input.KeyboardAccelerator sender, Microsoft.UI.Xaml.Input.KeyboardAcceleratorInvokedEventArgs args)
{
bool f = GridRoot.Focus(FocusState.Programmatic);
debug3.Text = "FOCUS DEBUG: " + f.ToString();
args.Handled = true;
}
```
### Why is this important?

Focus should return true if Focus has changed (i.e. User Presses Enter on a TextBox to change the title).

### Steps to reproduce the bug

1. In MainWIndow.xmal add x:Name to TextBox and an other element.
2. add the following xmal to TextBox
```



```
3. add the following code inside MainWindow.xaml.cs
```
private void TaskItemName_Enter(Microsoft.UI.Xaml.Input.KeyboardAccelerator sender, Microsoft.UI.Xaml.Input.KeyboardAcceleratorInvokedEventArgs args)
{
//Replace "GridRoot" with the element of your choice.
bool f = GridRoot.Focus(FocusState.Programmatic);
//either this or a debugger for the bool f.
debug3.Text = "FOCUS DEBUG: " + f.ToString();
args.Handled = true;
}
```
4. select TextBox and press ENTER
5. get the value of UIElement.Focus()
6. notice TextBox does not lose focus

### Actual behavior
Does not change focus despite returning true.

### Expected behavior
Changes focus or returns false.

### Screenshots

### NuGet package version

WinUI 3 - Windows App SDK 1.8.3: 1.8.251106002

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

_No response_

Reproduce the issue from MainWindow.xaml and MainWindow.xaml.cs using the provided KeyboardAccelerator and TaskItemName_Enter handler. Start by checking the return value and resulting focus after selecting the TextBox and pressing Enter; done means focus changes as expected or Focus returns false when it does not.

Written by the indexing model from the issue text.