[ISSUE #8372] Add more test coverage for AdminBrokerProcessor

[TanXiang7o]

fix #8372
before:

after:

[RongtongJin]

LGTM

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 44.39%. Comparing base (77f6415) to head (fb19731).
Report is 5 commits behind head on develop.

Files	Patch %	Lines
...ocketmq/broker/processor/AdminBrokerProcessor.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #8373      +/-   ##
=============================================
+ Coverage      44.03%   44.39%   +0.36%     
- Complexity     10683    10764      +81     
=============================================
  Files           1274     1274              
  Lines          88939    88939              
  Branches       11432    11432              
=============================================
+ Hits           39162    39486     +324     
+ Misses         44820    44471     -349     
- Partials        4957     4982      +25     

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[ShannonDing]

link #8262