test: fix unstable test TestFlashbackSchema (#50156)

[ti-chi-bot]

This is an automated cherry-pick of #50156

What problem does this PR solve?

Issue Number: close #50153

Problem Summary: Do not use image in TestFlashbackSchema, there may be some old ddl jobs causing get a wrong error in the tests.

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

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[ti-chi-bot]

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Adding the do-not-merge/cherry-pick-not-approved label.

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[codecov]

Codecov Report

Merging #50200 (9aff544) into release-7.6 (6701bf1) will increase coverage by 0.0002%.
The diff coverage is n/a.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release-7.6     #50200        +/-   ##
===================================================
+ Coverage      70.0225%   70.0227%   +0.0002%     
===================================================
  Files             1436       1436                
  Lines           419055     419055                
===================================================
+ Hits            293433     293434         +1     
+ Misses          105328     105327         -1     
  Partials         20294      20294                

Flag	Coverage Δ
unit	70.0227% <ø> (+0.0002%)	⬆️

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

Components	Coverage Δ
dumpling	54.0269% <ø> (ø)
parser	∅ <ø> (∅)
br	49.6680% <ø> (ø)