Old window gains focus and moves to foreground when opening new window in `NavigationView.ItemInvoked`

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### Describe the bug

When handling the `NavigationView.ItemInvoked` event to open a new window, the old window unexpectedly regains focus and moves to the foreground after the new window is shown. This disrupts the user experience as the old window should remain in its current state and not interfere with the new window. However, this issue does not occur when opening a new window inside the `NavigationViewItem.Tapped` event.

### Steps to reproduce the bug

``` xaml

```

```cs
private void NavigationView_ItemInvoked(NavigationView sender, NavigationViewItemInvokedEventArgs args)
{
new MainWindow().Activate();
}

private void NavigationViewItem_Tapped(object sender, TappedRoutedEventArgs e)
{
new MainWindow().Activate();
}
```

### Expected behavior

The new window should open and gain focus without affecting the old window's focus or Z-order.

### Screenshots

https://github.com/user-attachments/assets/dd8cb9f7-f7f5-4773-a589-8aecc7d76cfd

### NuGet package version

WinUI 3 - Windows App SDK 1.6.3: 1.6.241114003

### Windows version

Windows 11 (23H2): Build 22631

### Additional context

_No response_

Start by reproducing the supplied sample on Windows 11 with Windows App SDK 1.6.3, comparing windows opened from NavigationView.ItemInvoked and NavigationViewItem.Tapped. Trace the focus and Z-order behavior after Activate(); done when ItemInvoked opens the new window without the old window regaining focus or moving to the foreground.

Written by the indexing model from the issue text.