[release-21.0] Flaky test fixes (#16940)

[vitess-bot]

Description

This is a backport of #16940

[vitess-bot]

Review Checklist

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General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.43%. Comparing base (7908b43) to head (d0f410c).
Report is 2 commits behind head on release-21.0.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-21.0   #16960      +/-   ##
================================================
- Coverage         69.45%   69.43%   -0.02%     
================================================
  Files              1570     1570              
  Lines            203835   203841       +6     
================================================
- Hits             141564   141542      -22     
- Misses            62271    62299      +28     

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[deepthi]

Since this PR only touches test files, we have agreed that it can be merged into the release branch during freeze. cc @rohit-nayak-ps @frouioui