*: fix bug that table name in 'admin show ddl jobs' is missing for ongoing drop table operation (#42904)

[ti-chi-bot]

This is an automated cherry-pick of #42904

What problem does this PR solve?

Issue Number: close #42268

Problem Summary:

What is changed and how it works?

During drop table, the table is removed from the infoschema
So getTableName found nothing.
This cause the missing of the table name in 'admin show ddl jobs' result.

On the master branch, we can get the table name by job.TableName.
For older tidb, there is no TableName field, we need some other way to fix it.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Fix a bug that table name in 'admin show ddl jobs' is missing for ongoing drop table operation

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/build	8ae7726	link	true	/test build
idc-jenkins-ci-tidb/check_dev_2	8ae7726	link	true	/test check-dev2
idc-jenkins-ci-tidb/check_dev	8ae7726	link	true	/test check-dev
idc-jenkins-ci-tidb/mysql-test	8ae7726	link	true	/test mysql-test
idc-jenkins-ci-tidb/unit-test	8ae7726	link	true	/test unit-test

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