expression: fix wrong type infer for agg function when type is null (#24290)

[ti-srebot]

cherry-pick #24290 to release-5.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/24354

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---

Signed-off-by: lzmhhh123 [email protected]

What problem does this PR solve?

Issue Number: close #24264

What is changed and how it works?

What's Changed:

How it Works:

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Release note

• fix wrong type infer for agg function when type is null.

[ti-srebot]

/run-all-tests

[ti-srebot]

@lzmhhh123 you're already a collaborator in bot's repo.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• ichn-hu
• wshwsh12

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[qw4990]

/merge

[ti-chi-bot]

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

Commit hash: 8d77afa

[ti-chi-bot]

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