Fix panic on unsigned tinyint (#2649)

[ti-chi-bot]

This is an automated cherry-pick of #2649

What problem does this PR solve?

Closes #2648

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

Fix a bug that causes TiCDC to panic on an unsigned tinyint

[ti-chi-bot]

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[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: d156d5c

[amyangfei]

/run-integration-tests
/run-kafka-tests

[amyangfei]

/run-integration-tests

[amyangfei]

/merge

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@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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/run-all-tests

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[amyangfei]

/run-integration-tests

[amyangfei]

/run-integration-tests

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.1@6c35615). Click here to learn what that means.
The diff coverage is n/a.

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