Patterns in `.git/info/exclude` that contain a slash (e.g.
`.claude/worktrees`) are anchored: Git matches them relative to the
project root. Zed was instead matching them relative to the `.git/info/`
directory that the file lives in, so they matched nothing and had no
effect.

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:

- Support anchored patterns in .git/info/exclude

---------

Co-authored-by: Cole Miller <cole@zed.dev>
Co-authored-by: zed-zippy[bot] <234243425+zed-zippy[bot]@users.noreply.github.com>