Fixes
https://linear.app/zed-industries/issue/Z-2542/deleting-assistant-conversations-with-zed-open-can-cause-a-crash

We were updating the view's state but missed a `notify`, which caused
the `UniformList` responsible for rendering the saved conversations to
panic when some files were deleted.

Release Notes:

- Fixed a crash that could happen when deleting a saved assistant
conversation from the filesystem.