git_ui: Make git_ui call support optional (#58413)

Broke the headless builds for evals. Open to cleaner ways of doing
this...

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A
5efd6f68c7Ben Brandt committed on 6/3/2026, 1:18:45 PM· committed by GitHubparent6d72acd
4 files changedLine totals unavailable