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):

レポートにリンクされている Angular Material form-field のエラーメッセージの例から始め、NVDA を使用してその動作を再現します。フィールドがフォーカスを失ったときに表示されるエラーに重点を置いてください。アナウンスを期待される 1 回の読み上げと比較し、関係する form-field エラー表示経路を特定します。mat-error が 1 回だけアナウンスされ、文書化されている動作に退行がない状態を完了とします。

索引モデルが issue の本文から書いたものです。