statistics: add more test for tidb_merge_partition_stats_concurrency

[hawkingrei]

What problem does this PR solve?

Issue Number: close #48713

Problem Summary:

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[codecov]

Codecov Report

Merging #48965 (addcd5d) into master (ba608a9) will increase coverage by 1.6718%.
Report is 7 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #48965        +/-   ##
================================================
+ Coverage   70.9881%   72.6600%   +1.6718%     
================================================
  Files          1368       1389        +21     
  Lines        404890     412703      +7813     
================================================
+ Hits         287424     299870     +12446     
+ Misses        97444      93896      -3548     
+ Partials      20022      18937      -1085     

Flag	Coverage Δ
integration	43.6865% <ø> (?)
unit	70.9881% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9663% <ø> (ø)
parser	∅ <ø> (∅)
br	48.4613% <ø> (-4.6196%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qw4990, time-and-fate

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• OWNERS [qw4990,time-and-fate]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-29 05:53:33.86430552 +0000 UTC m=+988442.529531715: ☑️ agreed by qw4990.
• 2023-11-29 08:46:56.909509571 +0000 UTC m=+998845.574735747: ☑️ agreed by time-and-fate.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #49013.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #51158.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #51159.