Can't Change Shell FlyoutBackgroundColor From a Theme Style File

### Description

I would like to set the FlyoutBackgroundColor via Styles which does not seem to work.
According to [Issue 5808](https://github.com/dotnet/maui/issues/5808) this was already a problem which should be fixed... but isn't.

I'm using the latest VisualStudio version. I wasn't quite able to find out which .NET MAUI Version is shipped with VS 17.3.2... But the nuget-package version of `Microsoft.Maui.Dependencies` is 6.0.486

### Steps to Reproduce

1. In Visual Studio v17.3.2 create a new .NET MAUI project
2. Open AppShell.xaml
3. Change `Shell.FlyoutBehavior` to `Flyout`
4. Open Resources\Styles\Styles.xaml
5. In `` add `<Setter Property="Shell.FlyoutBackgroundColor" Value="Red" />`
6. Start App on Android, Windows, ...
7. Open the Flyout
8. Backgroundcolor is not red

Example: https://github.com/SokoFromNZ/FlyoutBackgroundColor

### Version with bug

6.0.486 (current)

### Last version that worked well

Unknown/Other

### Affected platforms

iOS, Android, Windows

### Affected platform versions

Android 11, Windows 10, iOS 15

### Did you find any workaround?

If you set the `FlyoutBackgroundColor` directly in AppShell.xaml it works.
Using `FlyoutBackground` instead works in Styles.xaml as well.

### Relevant log output

_No response_