tables: fix insert ignore on duplicate with dup prefix 2nd index (#25905)

[ti-srebot]

cherry-pick #25905 to release-3.0
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---

What problem does this PR solve?

Issue Number: close #25809

Problem Summary:

now it relies on modified array to decide whether skip modified index dup check after duplicate updated.

but when clustered primary key has same column with secondary index,and the column is prefix, changed in table doesn't indicate it be change in index.

What is changed and how it works?

What's Changed, How it Works:

truncate datum to index length and re-check modified for prefix column

Related changes

• Need to cherry-pick to the release branch 4.0, 3.0

Check List

Tests

• Unit test

Side effects

• n/a

Release note

• Fix the wrong result after "insert ignore on duplicate update" in the secondary index has the same column in primary key but has prefix length

[ti-chi-bot]

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[ti-chi-bot]

@ti-srebot: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[ti-srebot]

/run-all-tests

[ti-chi-bot]

@ti-srebot: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ti-srebot]

@lysu you're already a collaborator in bot's repo.

[lysu]

3.0 have no clustered index, there are no those problem