Before this PR we wouldn't always serialize workspaces when a mutliworkspace adds/removes a workspace. This PR fixes this by adding a test and calling serialization in remove 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 - [ ] Aligned any UI changes with the [UI checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist) Release Notes: - N/A