Update .env.testing

.env.testing

@@ -28,6 +28,8 @@ REDIS_HOST=127.0.0.1
 REDIS_PASSWORD=null
 REDIS_PORT=6379
 
+HORIZON_PREFIX="horizon-"
+
 MAIL_DRIVER=log
 MAIL_HOST=smtp.mailtrap.io
 MAIL_PORT=2525