planner: fix duplicated children id in optimizer trace

[Yisaer]

Signed-off-by: yisaer disxiaofei@163.com

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

What is changed and how it works?

Plan trace may has duplicated id in children, this request fixed it.

Check List

Tests

• Unit test

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:

• JmPotato
• hawkingrei

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[Yisaer]

/merge

[ti-chi-bot]

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

Commit hash: d850bcf

[hawkingrei]

TestFlattenLogicalPlanTrace is fail.

/hold

[Yisaer]

/merge

[ti-chi-bot]

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

Commit hash: 3dd71fa

[Yisaer]

/hold cancel

[Yisaer]

/merge

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [2] 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/integration-ddl-test	🔴 failed 1, success 5, total 6	23 min	Existing failure
idc-jenkins-ci-tidb/integration-common-test	🔴 failed 2, success 15, total 17	15 min	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 37 tests passed	26 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 11 tests passed	12 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	7 min 1 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	4 min 41 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	4 min 3 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 10 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 3 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed