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: d7ff708

[amyangfei]

/run-integration-tests

[codecov-commenter]

Codecov Report

Merging #2654 (d7ff708) into release-4.0 (753073a) will increase coverage by 1.4050%.
The diff coverage is 58.3333%.

@@                 Coverage Diff                 @@
##           release-4.0      #2654        +/-   ##
===================================================
+ Coverage      53.7661%   55.1711%   +1.4050%     
===================================================
  Files              153        164        +11     
  Lines            15958      19715      +3757     
===================================================
+ Hits              8580      10877      +2297     
- Misses            6475       7805      +1330     
- Partials           903       1033       +130