server: make clientConn() thread-safe (#49073)

[ti-chi-bot]

This is an automated cherry-pick of #49073

What problem does this PR solve?

Issue Number: ref #48224, #36793 and #32110

Problem Summary:

What changed and how does it work?

Please check #36793 (comment) for more details and context:

But for further enhancement, we cloud still try to make closeConn thread-safe.

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

• None

Documentation

• None

Release note

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

None

[bb7133]

/cherry-pick-invite

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@e30242b). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #49104   +/-   ##
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  Coverage               ?   73.6358%           
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  Lines                  ?     349436           
  Branches               ?          0           
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  Hits                   ?     257310           
  Misses                 ?      75615           
  Partials               ?      16511           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, tiancaiamao

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-12-04 06:24:24.761224156 +0000 UTC m=+1422293.426450349: ☑️ agreed by tiancaiamao.
• 2023-12-04 06:25:06.064524019 +0000 UTC m=+1422334.729750215: ☑️ agreed by lance6716.