This fixes the git blame sidebar looking wrong if the buffer font size
is higher than the UI font size (which is what was previously used).

It fixes this:

![screenshot-2024-03-28-19 46
48@2x](https://github.com/zed-industries/zed/assets/1185253/eca360ac-c8e8-41e0-85a1-52bdd05b9413)

To now look like this:

![screenshot-2024-03-28-19 47
42@2x](https://github.com/zed-industries/zed/assets/1185253/1fe93370-b7a2-44d4-a505-6368d72e2659)


Release Notes:

- N/A