worktree: Do not scan for .gitignore files beyond project root. (#8189)

This has been fixed and reported before (and got lost in gpui1->gpui2
transition);
https://github.com/zed-industries/zed/issues/5749#issuecomment-1959217319

Release Notes:

- Fixed .gitignore files beyond the first .git directory being respected
by the worktree (zed-industries/zed#5749).
94bc216bbdPiotr Osiewicz committed on 2/22/2024, 12:16:19 PM· committed by GitHubparent95d5ea7
1 file changedLine totals unavailable