expression: fix wrong result of greatest/least(mixed unsigned/signed int) (#30121)

[ti-srebot]

cherry-pick #30121 to release-5.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/30791

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git push git@github.com:ti-srebot/tidb.git pr/30791:release-5.0-4947cf1f596d

---

What problem does this PR solve?

Issue Number: close #30101

Problem Summary:

unsigned flag lost when building function.

What is changed and how it works?

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

Fix wrong result of greatest/least Function.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• guo-shaoge

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[ti-srebot]

/run-all-tests

[ti-srebot]

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

[XuHuaiyu]

LGTM

[XuHuaiyu]

/merge

[XuHuaiyu]

/merge

[zhouqiang-cl]

/merge

[XuHuaiyu]

/merge cancel

[XuHuaiyu]

/merge

[ti-chi-bot]

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

Commit hash: 3117d02

[ti-chi-bot]

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