Add missing type option for REST API endoint

Author: chriszarate

lib/experimental/sync/class-gutenberg-http-polling-sync-server.php

@@ -87,6 +87,7 @@ public function register_routes(): void {
 			),
 			'awareness' => array(
 				'required' => true,
+				'type'     => 'object',
 			),
 			'client_id' => array(
 				'minimum'  => 1,