sink: fix codec json encoding with non binary string (#2764)

[ti-chi-bot]

This is an automated cherry-pick of #2764

What problem does this PR solve?

Close #2758

Note we still don't known in which scenario the column value is string instead of []byte, need more investigation.

What is changed and how it works?

The column value type of mysql.TypeString, mysql.TypeVarString, mysql.TypeVarchar could be either string or []byte, we should consider both of these two types when converting a row column value to json encoding.

Check List

Tests

• Unit test
• Integration test

Release note

Fix json encoding could panic when processing a string type value in some cases.

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: 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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[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: b6d108a

[amyangfei]

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

[amyangfei]

/run-integration-tests

[codecov-commenter]

Codecov Report

Merging #2782 (b6d108a) into release-5.0 (0ebf717) will decrease coverage by 0.0195%.
The diff coverage is 75.0000%.

@@                 Coverage Diff                 @@
##           release-5.0      #2782        +/-   ##
===================================================
- Coverage      55.4760%   55.4564%   -0.0196%     
===================================================
  Files              165        165                
  Lines            19841      19848         +7     
===================================================
  Hits             11007      11007                
- Misses            7786       7793         +7     
  Partials          1048       1048