*: fix data race of TestRaftClusterMultipleRestart

[rleungx]

What problem does this PR solve?

Issue Number: Close #7391

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:

• CabinfeverB
• lhy1024

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[codecov]

Codecov Report

Merging #7392 (b647442) into master (dda748a) will increase coverage by 0.09%.
Report is 1 commits behind head on master.
The diff coverage is 86.25%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7392      +/-   ##
==========================================
+ Coverage   74.27%   74.36%   +0.09%     
==========================================
  Files         451      451              
  Lines       48967    49046      +79     
==========================================
+ Hits        36372    36475     +103     
+ Misses       9375     9357      -18     
+ Partials     3220     3214       -6     

Flag	Coverage Δ
unittests	74.36% <86.25%> (+0.09%)	⬆️

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[rleungx]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: b647442