fix fatal on WP_Error do to missing root namespace

Author: nerrad

src/RestApi/Controllers/ProductAttributes.php

@@ -79,7 +79,7 @@ public function register_routes() {
 	 */
 	public function get_items_permissions_check( $request ) {
 		if ( ! current_user_can( 'edit_posts' ) ) {
-			return new WP_Error( 'woocommerce_rest_cannot_view', __( 'Sorry, you cannot list resources.', 'woo-gutenberg-products-block' ), array( 'status' => rest_authorization_required_code() ) );
+			return new \WP_Error( 'woocommerce_rest_cannot_view', __( 'Sorry, you cannot list resources.', 'woo-gutenberg-products-block' ), array( 'status' => rest_authorization_required_code() ) );
 		}
 		return true;
 	}