expression: fix that the result of expression castRealAsTime is inconsistent with mysql (#37461)

[ti-srebot]

cherry-pick #37461 to release-5.1
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/37560

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---

What problem does this PR solve?

Issue Number: close #37462

Problem Summary:
fix that the result of expression castRealAsTime is inconsistent with mysql

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

Please refer to Release Notes Language Style Guide to write a quality release note.

fix that the result of expression castRealAsTime is inconsistent with mysql.

[ti-srebot]

/run-all-tests

[ti-chi-bot]

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[ti-srebot]

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