bug(Chips): Selecting value from autocomplete by keyboard navigation causes both the search string and the selected option to be added

### 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

Reproducible on this [example](https://material.angular.io/components/chips/overview#chips-autocomplete).

### Reproduction

StackBlitz link: https://stackblitz.com/edit/rd9usi?file=package.json
Steps to reproduce:
1. Type any input that is a substring of any item in the suggestion list
2. Navigate to a suggestion with keyboard
3. Press Enter
4. Both the search string and the selected are added

### Expected Behavior

Only the selected suggestion is added

### Actual Behavior

Both the selected and the suggested values are added

### Environment

- Angular: 16.2.6
- CDK/Material: 16.2.8
- Browser(s): Google Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): darwin arm64

Start with the linked StackBlitz reproduction, including package.json, and compare its behavior with the Chips autocomplete example. Trace keyboard navigation and Enter handling for a typed substring, then verify that only the selected suggestion is added and the search string is not also added.

Written by the indexing model from the issue text.