expression: fix date format identifies '\n' as invalid separator (#32358)

[ti-srebot]

cherry-pick #32358 to release-5.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/32376

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git push git@github.com:ti-srebot/tidb.git pr/32376:release-5.0-2b9093f30d07

---

What problem does this PR solve?

fix date formate identifies '\n' is invalid separator

Issue Number: close #32232

Problem Summary:

What is changed and how it works?

builtin_time.go

Check List

Tests

• Unit test

Release note

fix date formate identifies '\n' as invalid separator

[ti-chi-bot]

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[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

/run-all-tests

[ti-srebot]

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