Accessibility issues with reading the invisible Title bar using Narrator.

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### Describe the bug

When I customize my Title bar, using the ExtendsContentIntoTitleBar = true property and activating Narrator (Ctrl+Windows+Enter), the window reads normally.

However, if I activate Scan Mode (Caps Lock + Spacebar) after navigating to the last control on the screen, be it a text field, button, or anything else, Narrator starts reading an invisible title bar.

### Steps to reproduce the bug

Create a new project in WinUI 3.

Add any control to the screen, either a button or a text field.

Activate Narrator by pressing Ctrl+Windows+Enter.

Activate scan mode by pressing Caps Lock+Spacebar.

Navigate the screen using the up and down arrow keys.

### Expected behavior

The correct way would be to read only the first customized Title bar, and at the end of the screen, Narrator should display a "No next item" warning.

### Screenshots

_No response_

### NuGet package version

WinUI 3 - Windows App SDK 1.7.3: 1.7.250606001

### Windows version

Windows 11 (23H2): Build 22631

### Additional context

_No response_

Reproduce the issue in a new WinUI 3 project using Windows App SDK 1.7.3 on Windows 11 23H2. Enable ExtendsContentIntoTitleBar, run Narrator in Scan Mode, and navigate with the arrow keys after the last control. Done means Narrator reads only the customized title bar and then reports no next item.

Written by the indexing model from the issue text.