Fix lightning bolt hover and git gutter mark overlapping (#4195)

Bumps `gutter_padding_factor` from 3.5 to 4.0 due git mark on the gutter
becoming much thicker than in Zed1:
 
Current:

![current_zed_2](https://github.com/zed-industries/zed/assets/2690773/f7f0f76b-63a2-4790-a4f4-ca791b617a64)

Fixed:

![new_zed2](https://github.com/zed-industries/zed/assets/2690773/0075567d-e661-4140-8ffa-ec17d72f8e54)

Stable (no hover background appearing):

![zed_1](https://github.com/zed-industries/zed/assets/2690773/c3366845-b763-46f7-a2c7-48dd72dc4f10)

Release Notes:

- Fixed gutter marks overlapping with hover highlights