syncer: don't skip jobs from same event when comparing table checkpoint

[lance6716]

What problem does this PR solve?

close #1751

after all_mode paused, we could see

MySQL [all_mode]> select * from t2;
+----+-------+---------------------+
| id | name  | ts                  |
+----+-------+---------------------+
|  1 | Arya  | 2021-06-05 18:01:52 |
|  2 | Bran  | 2021-05-11 10:01:05 |
|  3 | Sansa | 2021-06-05 18:01:52 |
| 10 | 10    | 2021-06-05 18:02:02 |
| 20 | 20    | 2021-06-05 18:02:02 |
| 30 | 30    | 2021-06-05 18:02:02 |
+----+-------+---------------------+
6 rows in set (0.001 sec)

MySQL [all_mode]> select * from t1;
+----+---------+---------------------+---------------------+
| id | name    | dt                  | ts                  |
+----+---------+---------------------+---------------------+
|  1 | ar"ya   | 2021-06-05 18:01:52 | 2021-06-05 18:01:52 |
|  2 | catelyn | 2021-05-11 10:01:05 | 2021-05-11 10:01:05 |
|  3 | lalala  | NULL                | 2021-06-05 18:01:52 |
| 10 | 10      | NULL                | 2021-06-05 18:02:01 |
| 30 | 30      | NULL                | 2021-06-05 18:02:02 |
+----+---------+---------------------+---------------------+
5 rows in set (0.001 sec)

t1 losts a row with id = 20 of https://github.com/pingcap/dm/pull/1752/files#diff-5cc7189b51f6219ea0ce1c9920f92f84cee41b3fee093894a72ca5ff1c615b4aR2

What is changed and how it works?

Check List

Tests

• Integration test

Code changes

• Has interface methods change

Related changes

• Need to cherry-pick to the release branch
• Need to be included in the release note

[GMHDBJD]

LGTM

[Ehco1996]

rest LGTM

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[glorv]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 4c80409

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1781.