tests: make TestFallbackTSOConsistency stable

[lhy1024]

What problem does this PR solve?

Issue Number: Close #7407

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• rleungx

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[JmPotato]

Why not just use testutil.Eventually?

[JmPotato]

Why not just use the original package name?

[lhy1024]

In most places, it is called tu

[codecov]

Codecov Report

Merging #7408 (0afb184) into master (57fb020) will decrease coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7408      +/-   ##
==========================================
- Coverage   74.28%   74.25%   -0.04%     
==========================================
  Files         451      451              
  Lines       49174    49174              
==========================================
- Hits        36527    36512      -15     
- Misses       9423     9429       +6     
- Partials     3224     3233       +9     

Flag	Coverage Δ
unittests	74.25% <ø> (-0.04%)	⬇️

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[lhy1024]

/merge

[ti-chi-bot]

@lhy1024: It seems you want to merge this PR, I will help you trigger all the tests:

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[ti-chi-bot]

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

Commit hash: 0afb184