core: fix datarace in MergeLabels (#7537)

[ti-chi-bot]

This is an automated cherry-pick of #7537

What problem does this PR solve?

Issue Number: Close #7535

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
• rleungx

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[codecov]

Codecov Report

Merging #7830 (94bab38) into release-7.5 (3488a65) will increase coverage by 0.02%.
Report is 1 commits behind head on release-7.5.
The diff coverage is 100.00%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-7.5    #7830      +/-   ##
===============================================
+ Coverage        74.53%   74.56%   +0.02%     
===============================================
  Files              444      444              
  Lines            48140    48154      +14     
===============================================
+ Hits             35882    35906      +24     
+ Misses            9073     9058      -15     
- Partials          3185     3190       +5     

Flag	Coverage Δ
unittests	74.56% <100.00%> (+0.02%)	⬆️

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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: 94bab38