[BUG] Expander: BoxView Inside expander isn't rendered on iOS

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Did you read the "Reporting a bug" section on Contributing file?

- [x] I have read the "Reporting a bug" section on Contributing file: https://github.com/CommunityToolkit/Maui/blob/main/CONTRIBUTING.md#reporting-a-bug

### Current Behavior

We use Expander component and inside it we use a BoxView with HeightRequest = 1, as a seperator. On iOS, the BoxView isn't rendered. If I switch from white to dark mode ** while the Expander is expanded**, it is rendered successfully.
On Android this behavior is not reproduced

I have created a sample repository, this bug is also reproduced on our production app.

iOS:
https://github.com/user-attachments/assets/aed18af9-b604-46bf-87bf-0973ce64b170

Android:
https://github.com/user-attachments/assets/28fb749f-7a8c-4b34-9abb-30093b7429ba

### Expected Behavior

The Boxview should be correctly rendered on iOS when inside an expander (as it does on Android)

### Steps To Reproduce

1. Download repo on Mac and Build on iOS
2. Expand expander(the boxview is not rendered)
3. Switch to dark mode
4. The boxview is rendered

### Link to public reproduction project repository

https://github.com/cvchris/CommunityToolkit.Maui.ExpanderBug

### Environment

```markdown
- .NET MAUI CommunityToolkit: 12.1.0
- OS: iOS 18.5 / Android 15
- .NET MAUI:
.Net Maui 9.0.90
```

### Anything else?

_No response_

Start with the public reproduction project, CommunityToolkit.Maui.ExpanderBug, and build it on iOS using the reported .NET MAUI and CommunityToolkit versions. Reproduce the Expander with a one-pixel BoxView, then compare the iOS and Android behavior. Done means the BoxView renders when the Expander is opened on iOS without requiring a dark-mode switch.

Written by the indexing model from the issue text.