bug(drag-drop): cdkDropListSortPredicate doesn't work if dragging item enter from top

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

`cdkDropListSortPredicate` doesn't work in certain senarios

### Reproduction

StackBlitz link: https://stackblitz.com/edit/z6ffpx7e-wg8uidxw?file=src%2Fexample%2Fcdk-drag-drop-connected-sorting-group-example.html
Steps to reproduce:
1. Open StackBlitz reproduction link
2. The code has `cdkDropListSortPredicate` applied to "Done" dropzone, the intention is preventing item being dragged to the first index
3. Drag item from "To do" zone and enter "Done" zone from top


### Expected Behavior

Item cannot be dragged & dropped to the first index in "Done"

### Actual Behavior

Item can be dragged & dropped to the first index in "Done"

### Environment

- Angular: 19.0.0
- CDK/Material: 19.0.0
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

Comienza con la reproducción enlazada de StackBlitz e inspecciona el comportamiento de cdkDropListSortPredicate cuando un elemento entra en la dropzone Done desde arriba. Reproduce el caso en Angular 19.0.0 y verifica después que el predicate impide que el elemento se suelte en el primer índice, preservando el resto del comportamiento de ordenación.

Escrito por el modelo de indexación a partir del texto del issue.