test: improve some tests

[xiongjiwei]

What problem does this PR solve?

Issue Number: ref #32031

Problem Summary:

• use the real session instead mock session
• commit some txn explicitly
• add GetLastHistoryDDLJobsIterator to wrap the get iterator, make it easy to change implementation to concurrent ddl in the future

Tests

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

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
• wjhuang2016

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/726cb5f78c4a9f92045be1c7d96a38ccc6510daf

[xiongjiwei]

/run-check_dev_2

[hawkingrei]

/merge

[ti-chi-bot]

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

Commit hash: 2575811

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-ddl-test	🟥 failed 1, success 5, total 6	6 min 19 sec	New failing
idc-jenkins-ci/integration-cdc-test	🟢 all 35 tests passed	30 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 11 tests passed	14 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 12 tests passed	7 min 6 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	6 min 5 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	5 min 27 sec	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	4 min 49 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 18 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 6 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed