Closes #50880 

When a git worktree linked via a `.git` file (e.g. `gitdir:
/repo/.git/worktrees/my-worktree`) was opened in Zed, entries in
`.git/info/exclude` were not respected. This is now fixed.

Before you mark this PR as ready for review, make sure that you have:
- [x] Added a solid test coverage and/or screenshots from doing manual
testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- Fixed `.git/info/exclude` not being respected when opening a secondary
git worktree


https://github.com/user-attachments/assets/f38df5dc-96eb-40a8-a77c-0932a2c8575b

---------

Co-authored-by: Lukas Wirth <lukas@zed.dev>
Co-authored-by: Lukas Wirth <me@lukaswirth.dev>