mcs: make TestDefaultKeyspaceGroup stable

[rleungx]

What problem does this PR solve?

Issue Number: Close #7374.

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:

• lhy1024

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[rleungx]

/merge

[ti-chi-bot]

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

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 5a85b97

[ti-chi-bot]

@rleungx: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[codecov]

Codecov Report

Merging #7437 (5a85b97) into master (eafc1ed) will decrease coverage by 0.03%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

❗ Current head 5a85b97 differs from pull request most recent head acb8f68. Consider uploading reports for the commit acb8f68 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7437      +/-   ##
==========================================
- Coverage   74.22%   74.19%   -0.03%     
==========================================
  Files         451      451              
  Lines       49530    49530              
==========================================
- Hits        36762    36751      -11     
- Misses       9479     9481       +2     
- Partials     3289     3298       +9     

Flag	Coverage Δ
unittests	74.19% <ø> (-0.03%)	⬇️

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