ddl: fixed an issue with using different time zones when changing timestamp types to other types

[zimulala]

What problem does this PR solve?

Issue Number: close #29585

Problem Summary:

What is changed and how it works?

Use the same time zone when changing the timestamp type to another type.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Release note

Fixed an issue with using different time zones when changing timestamp types to other types

[ti-chi-bot]

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