message: Search for root manifest with ephemeral workspaces
  Fixes
diff: @@ -198,7 +198,9 @@ impl<'cfg> Workspace<'cfg> {
  target_dir: Option<Filesystem>,
  require_optional_deps: bool,
  ) -> CargoResult<Workspace<'cfg>> {
  - let mut ws = Workspace::new_default(package.manifest_path().to_path_buf(), config);
  + let manifest_path = package.manifest_path();
  + let mut ws = Workspace::new_default(manifest_path.to_path_buf(), config);
  + ws.root_manifest = ws.find_root(&manifest_path)?;
  ws.is_ephemeral = true;
  ws.require_optional_deps = require_optional_deps;
  let key = ws.current_manifest.parent().unwrap();
  