[fix][broker] fix flaky test in SystemTopicBasedTopicPoliciesServiceTest

[TakaHiR07]

Main Issue: #25081

Motivation

fix for flaky test.

Modifications

Verifying this change

• Make sure that the change passes the CI checks.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[lhotari]

LGTM

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.42%. Comparing base (df89b60) to head (6a15d2c).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##             master   #25098    +/-   ##
==========================================
  Coverage     74.42%   74.42%            
+ Complexity    34053    33658   -395     
==========================================
  Files          1899     1899            
  Lines        149659   149659            
  Branches      17394    17394            
==========================================
+ Hits         111389   111391     +2     
+ Misses        29396    29392     -4     
- Partials       8874     8876     +2     

Flag	Coverage Δ
inttests	26.69% <ø> (?)
systests	23.00% <ø> (-0.05%)	⬇️
unittests	73.96% <ø> (-0.06%)	⬇️

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see 104 files with indirect coverage changes

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