git_graph: Show propagated errors from git binary command (#53320)

Based on commit fba49809b39b0f9e58d68e3956f5c24fd47121d7 that I worked
with Dino on in PR: #50288

Co-authored-by Dino \<Dino@zed.dev\>

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

Closes #ISSUE

Release Notes:

- N/A or Added/Fixed/Improved ...
70d6c2bdc4Anthony Eid committed on 4/7/2026, 4:18:15 PM· committed by GitHubparent4f3e4d2
4 files changedLine totals unavailable