Improve VCS Menu header top margin. (#8879)

## Before

![SCR-20240305-nga](https://github.com/zed-industries/zed/assets/5518/e814d770-a5b1-4289-acc4-808bf7d96690)

![SCR-20240305-nge](https://github.com/zed-industries/zed/assets/5518/abba4f7c-7e6c-447f-8e4f-fbecdf802f62)

## After

![SCR-20240305-nfp](https://github.com/zed-industries/zed/assets/5518/5539b15c-c67d-466b-9c46-44e488788b04)

![SCR-20240305-nfu](https://github.com/zed-industries/zed/assets/5518/5cfdf861-b55c-4f1e-a41f-dcd42a449488)

Release Notes:

- Improve VCS Menu header top margin, and use `TextMuted` color for
matched count label.
6a268e959fJason Lee committed on 3/5/2024, 9:19:52 AM· committed by GitHubparent4b2e774
1 file changedLine totals unavailable