`mysql.analyze_jobs` missed indexes

[winoros]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

https://github.com/winoros/tidb/blob/debugging/pkg/statistics/handle/autoanalyze/priorityqueue/interval.go

Some internal SQLs're running on the table mysql.analyze_jobs.

But, this table only has one index.

CREATE TABLE `analyze_jobs` (
  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `table_schema` char(64) NOT NULL DEFAULT '',
  `table_name` char(64) NOT NULL DEFAULT '',
  `partition_name` char(64) NOT NULL DEFAULT '',
  `job_info` text NOT NULL,
  `processed_rows` bigint unsigned NOT NULL DEFAULT '0',
  `start_time` timestamp NULL DEFAULT NULL,
  `end_time` timestamp NULL DEFAULT NULL,
  `state` enum('pending','running','finished','failed') NOT NULL,
  `fail_reason` text DEFAULT NULL,
  `instance` varchar(512) NOT NULL COMMENT 'address of the TiDB instance executing the analyze job',
  `process_id` bigint unsigned DEFAULT NULL COMMENT 'ID of the process executing the analyze job',
  PRIMARY KEY (`id`) /*T![clustered_index] CLUSTERED */,
  KEY `update_time` (`update_time`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin AUTO_INCREMENT=901003903

As a result, we'll see a lot of full scan in a big cluster testing.

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

master