RadioButtons SelectionChanged trigger twice

Nobody has claimed this yet.

### Describe the bug

This has been an issue in UWP in #3128 , and someone was even kind enough to make a PR to fix it #3137 , but you guys just closed it because winui2 is no longer developed? And don't even check for it in winui3? So I just wasted another hour stumble upon this issue in WinUI3.

### Steps to reproduce the bug

1. Create a new winui3 project
2. In `MainWindow.xaml` use this code
```xml




```
3. In the handler code, just add a debug print.
4. The initial selection will trigger it once as expected. Select another item, this event handler will be triggered twice.

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

WinUI 3 - Windows App SDK 1.5.6: 1.5.240802000

### Windows version

Windows 11 (22H2): Build 22621

### Additional context
[Repro](https://github.com/HO-COOH/WinUI-Bug/tree/main/16-RadioButtonsSelectionChangedTriggerTwice)

Begin with the repro's MainWindow.xaml and RadioButtons_SelectionChanged handler, then run it against Windows App SDK 1.5.6 to confirm the duplicate event. Trace the RadioButtons selection-change path and verify that selecting another item produces one SelectionChanged callback, while the initial selection still behaves as expected.

Written by the indexing model from the issue text.