variable: fix data race in GetTemporaryTable (#55338)

[ti-chi-bot]

This is an automated cherry-pick of #55338

What problem does this PR solve?

Issue Number: close #55337

What changed and how does it work?

fix data race for TxnCtx.GetTemporaryTable

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

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-8.1@f29a4ea). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #55342   +/-   ##
================================================
  Coverage               ?   71.1619%           
================================================
  Files                  ?       1466           
  Lines                  ?     422681           
  Branches               ?          0           
================================================
  Hits                   ?     300788           
  Misses                 ?     101399           
  Partials               ?      20494           

Flag	Coverage Δ
unit	71.1619% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9656% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.3049% <0.0000%> (?)

[bb7133]

LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-09 15:23:56.960464527 +0000 UTC m=+624766.827563607: ☑️ agreed by lcwangchao.
• 2024-08-12 02:09:18.405737006 +0000 UTC m=+147443.109206649: ☑️ agreed by bb7133.

[easonn7]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bb7133, easonn7, lcwangchao

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• pkg/sessionctx/variable/OWNERS [easonn7]

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[lcwangchao]

/retest