test: fix unstable test TestClearCache (#51480)

[ti-chi-bot]

This is an automated cherry-pick of #51480

What problem does this PR solve?

Issue Number: close #50743

Problem Summary:

What changed and how does it work?

Fix unstable test of clear cache.

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-7.5@7ece220). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #53448   +/-   ##
================================================
  Coverage               ?   72.3227%           
================================================
  Files                  ?       1411           
  Lines                  ?     413661           
  Branches               ?          0           
================================================
  Hits                   ?     299171           
  Misses                 ?      94538           
  Partials               ?      19952           

Flag	Coverage Δ
unit	72.3227% <ø> (?)

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

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.4318% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3pointer, BornChanger

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• br/OWNERS [3pointer,BornChanger]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-21 10:13:50.650058308 +0000 UTC m=+2166584.407193884: ☑️ agreed by BornChanger.
• 2024-05-23 10:11:24.541135899 +0000 UTC m=+2339238.298271473: ☑️ agreed by 3pointer.