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: 1f66cb5

[amyangfei]

/run-integration-tests

[codecov-commenter]

Codecov Report

Merging #2657 (1f66cb5) into release-5.2 (81c22b1) will increase coverage by 0.0623%.
The diff coverage is 100.0000%.

@@                 Coverage Diff                 @@
##           release-5.2      #2657        +/-   ##
===================================================
+ Coverage      55.8716%   55.9340%   +0.0623%     
===================================================
  Files              169        169                
  Lines            20667      20669         +2     
===================================================
+ Hits             11547      11561        +14     
+ Misses            8012       8002        -10     
+ Partials          1108       1106         -2