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

从链接的 StackBlitz 复现开始，检查项目从顶部进入 Done dropzone 时 cdkDropListSortPredicate 的行为。在 Angular 19.0.0 中复现该情况，然后验证 predicate 是否会阻止项目被放置在第一个索引处，同时保留其他排序行为。

由索引模型根据 Issue 内容生成。