Grouped CollectionView not triggering Scrolled-Event for empty groups on iOS

### Description

We implemented lazyloading by listening to the scrolled event. When its triggered we check how much data is displayed and change it how we need it. Now i found an issue on ios that when there are only groups with no items the scrolled event is not triggered. The event is triggered correctly on android.

#22630 was maybe a similar issue
#10078 Issue with threshold in collectionviews

dotnet workload list:

### Steps to Reproduce

1. Clone repo
2. Run repo
3. Scroll

### Link to public reproduction project repository

https://github.com/SchittkowskiMS/MauiCollectionViewScrolledEvent

### Version with bug

9.0.50 SR5

### Is this a regression from previous behavior?

Not sure, did not test other versions

### Last version that worked well

Unknown/Other

### Affected platforms

iOS

### Affected platform versions

18.5

### Did you find any workaround?

No

### Relevant log output

```shell

```

Start with the public reproduction project linked in the issue and verify the behavior on iOS 18.5, then compare it with Android where the event works. Trace the grouped CollectionView scrolling behavior for groups without items; done means the Scrolled event fires when scrolling those empty groups on iOS without breaking the Android behavior.

Written by the indexing model from the issue text.