Bring back zed.rs tests (#3907)

At present 3 tests still fail; 2 are related to keymap issues that (I
believe) @maxbrunsfeld is working on. The other one
(`test_open_paths_action`) I'll look into. edit: done
This PR also fixes workspace unregistration, as we've put the code to do
that behind `debug_assert`
(https://github.com/zed-industries/zed/pull/3907/files#diff-041673bbd1947a35d45945636c0055429dfc8b5985faf93f8a8a960c9ad31e28L649).
Release Notes:
- N/A

crates/workspace/src/workspace.rs

@@ -658,7 +658,7 @@ impl Workspace {
             cx.on_release(|this, window, cx| {
                 this.app_state.workspace_store.update(cx, |store, _| {
                     let window = window.downcast::<Self>().unwrap();
-                    debug_assert!(store.workspaces.remove(&window));
+                    store.workspaces.remove(&window);
                 })
             }),
         ];