project_panel: Color worktree-modified files as modified, not warning (#57716)

I use the One Dark theme, so to actually test if my fix worked, I had to
also do:

```jsonc
"experimental.theme_overrides": {
  "warning": "#ff0000",
  "modified": "#00ff00",
},
```

| Before | After |
|--------|--------|
| <img width="676" height="254" alt="image"
src="https://github.com/user-attachments/assets/a2831667-1113-49ac-b6aa-1221c71bf997"
/> | <img width="299" height="137" alt="image"
src="https://github.com/user-attachments/assets/ad6e85aa-ba24-47ad-b69d-6d0c3aa3a407"
/> |

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] 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
- [ ] Performance impact has been considered and is acceptable

Closes #57443.

Release Notes:

- Fixed Project Panel git status indicator showing modified files with a
warning color instead of the modified color

crates/project_panel/src/project_panel.rs

@@ -7365,7 +7365,7 @@ fn git_status_indicator(git_status: GitSummary) -> Option<(&'static str, Color)>
         return Some(("D", Color::Deleted));
     }
     if git_status.worktree.modified > 0 {
-        return Some(("M", Color::Warning));
+        return Some(("M", Color::Modified));
     }
     if git_status.index.deleted > 0 {
         return Some(("D", Color::Deleted));