perf(db): 优化 xxl-job 数据库表索引结构

doc/db/tables_xxl_job.sql

@@ -100,8 +100,8 @@ CREATE TABLE `xxl_job_log`
     PRIMARY KEY (`id`),
     KEY `I_trigger_time` (`trigger_time`),
     KEY `I_handle_code` (`handle_code`),
-    KEY `I_jobid_jobgroup` (`job_id`,`job_group`),
+    KEY `I_jobgroup` (`job_group`),
-    KEY `I_job_id` (`job_id`)
+    KEY `I_jobid` (`job_id`)
 ) ENGINE = InnoDB
   DEFAULT CHARSET = utf8mb4;