## Context

This PR adds an action that only closes the sidebar, rather than always
toggling.

## Self-Review Checklist

<!-- Check before requesting review: -->
- [X] I've reviewed my own diff for quality, security, and reliability
- [N/A] Unsafe blocks (if any) have justifying comments
- [N/A] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [N/A ] Tests cover the new/changed behavior
- [N/A] Performance impact has been considered and is acceptable

Release Notes:

- Added a `multi workspace: close workspace sidebar` action.