ddl: skip the error when fallback from ingest to txn method

[Benjamin2037]

What problem does this PR solve?

Issue Number: ref #39321

Problem Summary:
When set fast reorg variable on, some ut will failed.

What is changed and how it works?

TestCancel
TestMultiSchemaChangeAddIndexesCancelled
TestCancelAddIndexPanic
TestDDLStatsInfo
TestPartitionAddIndexGC

This four case is dur to pd create rollback DDL, we set err to nil and DDL task will be resumed and executed later

TestRunDDLJobPanicEnableClusteredIndex
TestRunDDLJobPanicDisableClusteredIndex

skip merge woker number checker.

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.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• tangenta

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[Benjamin2037]

/run-check_dev_2

[Benjamin2037]

/run-check_dev_2

[Benjamin2037]

/run-check_dev_2

[Benjamin2037]

/run-check_dev_2

[Benjamin2037]

/run-check_dev_2

[Benjamin2037]

/run-check_dev_2

[Benjamin2037]

/run-all-tests

[wuhuizuo]

/run-all-tests

[wuhuizuo]

/run-all-tests

[wuhuizuo]

/run-build

[Benjamin2037]

/run-mysql-test

[Benjamin2037]

/merge

[ti-chi-bot]

@Benjamin2037: /merge is only allowed for the committers, you can assign this pull request to the committer in list by filling /assign @committer in the comment to help merge this pull request.

In response to this:

/merge

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[hawkingrei]

/merge

[ti-chi-bot]

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

Commit hash: ebc9852

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [1] CI still failing after this pr merged.
These failed integration tests don't seem to be introduced by the current PR.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/mybatis-test	🔴 failed 1, success 0, total 1	11 min	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 39 tests passed	21 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	17 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 11 tests passed	11 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 4 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	5 min 13 sec	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	5 min 4 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	4 min 34 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	2 min 55 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed