Make sure that we never write thread metadata to the DB for a thread
running on a collab project.

When joining a collab project and starting a native thread we would set
all your threads that had no paths associated with to the path of the
collab project (in `move_thread_paths`).

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:

- N/A