test(dm): try fix testMaster.TestStartTaskWithRemoveMeta

[Ehco1996]

What problem does this PR solve?

Issue Number: close #4168

What is changed and how it works?

the old test logic mute startTask err when chekcer failed, we should not do this, but i still not found why startTask failed

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to update key monitor metrics in both TiCDC document and official document

Release note

`None`.

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[lance6716]

ping @Ehco1996

[codecov-commenter]

Codecov Report

Merging #4306 (c5d025d) into master (08da001) will increase coverage by 0.2530%.
The diff coverage is 52.1359%.

Flag	Coverage Δ
cdc	59.2912% <63.4101%> (+0.6464%)	⬆️
dm	52.1870% <39.5897%> (-0.0676%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             master      #4306        +/-   ##
================================================
+ Coverage   55.1722%   55.4253%   +0.2530%     
================================================
  Files           485        495        +10     
  Lines         59829      60918      +1089     
================================================
+ Hits          33009      33764       +755     
- Misses        23484      23765       +281     
- Partials       3336       3389        +53     

[Ehco1996]

Close for now, still no way to reproduce locally