Setting Background on GridSplitter breaks Style

### Describe the bug

Setting the Background Property on the GridSplitter breaks the Style when hovering over the GridSplitter.
The Colour of the Splitter seems to flicker:

The problem appears both in dark and light Themes:

### Steps to reproduce

```text

Click Me

Click Me 2

```

### Expected behavior

I expect the GridSplitter to support a custom Background without flickering

### Screenshots

_No response_

### Code Platform

- [ ] UWP
- [X] WinAppSDK / WinUI 3
- [ ] Web Assembly (WASM)
- [ ] Android
- [ ] iOS
- [ ] MacOS
- [ ] Linux / GTK

### Windows Build Number

- [ ] Windows 10 1809 (Build 17763)
- [ ] Windows 10 1903 (Build 18362)
- [ ] Windows 10 1909 (Build 18363)
- [ ] Windows 10 2004 (Build 19041)
- [ ] Windows 10 20H2 (Build 19042)
- [ ] Windows 10 21H1 (Build 19043)
- [ ] Windows 10 21H2 (Build 19044)
- [ ] Windows 10 22H2 (Build 19045)
- [ ] Windows 11 21H2 (Build 22000)
- [X] Other (specify)

### Other Windows Build number

Windows 11 23H2 (Build 22631)

### App minimum and target SDK version

- [X] Windows 10, version 1809 (Build 17763)
- [ ] Windows 10, version 1903 (Build 18362)
- [ ] Windows 10, version 1909 (Build 18363)
- [ ] Windows 10, version 2004 (Build 19041)
- [ ] Windows 10, version 2104 (Build 20348)
- [ ] Windows 11, version 22H2 (Build 22000)
- [ ] Other (specify)

### Other SDK version

_No response_

### Visual Studio Version

2022

### Visual Studio Build Number

17.9.1

### Device form factor

Desktop

### Additional context

_No response_

### Help us help you

No, I'm unable to contribute a solution.