Revert to fix panic in inline assistant (#28428)

This reverts commit f12a554f86, which
introduced a panic in inline assistant (cc @mgsloan) - I'm not sure what
the motivation was for that change, but I figure we can revert to fix
the inline assistant now and deal with that later. 😄

Panic was:

> Thread "main" panicked with "cannot read workspace::Workspace while it
is already being updated" at
/Users/rtfeldman/code/zed/crates/gpui/src/app/entity_map.rs:139:32


Release Notes:

- N/A

crates/agent/src/context_picker/completion_provider.rs

@@ -867,7 +867,7 @@ mod tests {
                 .expect("Opened test file wasn't an editor")
         });
 
-        let context_store = cx.new(|_| ContextStore::new(project.downgrade(), None));
+        let context_store = cx.new(|_| ContextStore::new(workspace.downgrade(), None));
 
         let editor_entity = editor.downgrade();
         editor.update_in(&mut cx, |editor, window, cx| {