bug(mat-error): mat-error presentation is announces twice with NVDA screen reader

### Is this a regression?

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

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

@angular/material 18.1.0 did not have this behavior

### Description

Hi,

I am using NVDA v2025.3 (latest version) for accessibility testing and have noticed that the mat-error presentation is announced twice by the screen reader.

The above example demonstrates the issue from the angular material docs:
https://material.angular.dev/components/form-field/overview#error-messages

### Reproduction

Steps to reproduce:
1. Open screen reader and set focus on an angular material mat-form-field with mat-error presented on blur
2. Tab away from the field to trigger error message presentation
3. Observe announcements and notice that mat-error text is read twice.

### Expected Behavior

mat-errors should only be announced a single time by the screen reader.

### Actual Behavior

mat-error is announced twice by the screen reader.

### Environment

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

从报告中链接的 Angular Material form-field 错误消息示例开始，使用 NVDA 重现该行为，重点关注字段失去焦点时显示的错误。将播报与预期的单次读取进行比较，并确定涉及的 form-field 错误呈现路径；完成的标准是 mat-error 只播报一次，且不回归文档所述的行为。

由索引模型根据 Issue 内容生成。