gpui: Fix text underline width (#26827)

Release Notes:

- N/A 

Fix #24721 mistake to make sure underline width same as the text.

## Before


![image](https://github.com/user-attachments/assets/1fe6a8c2-517f-41be-bdf0-0ee777b7f8aa)

## After

<img width="912" alt="image"
src="https://github.com/user-attachments/assets/222b5dcb-c0fb-4ec1-8e23-d68247621375"
/>
b81a1ad91dJason Lee committed on 3/15/2025, 4:18:11 PM· committed by GitHubparent5f390f1
1 file changedLine totals unavailable