fix: json.mget should be readonly (redis#2807) (redis#2808)

* fix: json.mget should be readonly (redis#2807)

* lint

Author: marcoreni

packages/json/lib/commands/MGET.ts

@@ -2,6 +2,8 @@ import { RedisJSON, transformRedisJsonNullReply } from '.';
 
 export const FIRST_KEY_INDEX = 1;
 
+export const IS_READ_ONLY = true;
+
 export function transformArguments(keys: Array<string>, path: string): Array<string> {
     return [
         'JSON.MGET',