[ISSUE #7302] Fix singleTopicRegister code deleted in merge

[yuz10]

Which Issue(s) This PR Fixes

Fixes #7302

Brief Description

How Did You Test This Change?

[codecov-commenter]

Codecov Report

Merging #7303 (3ada83f) into develop (d000ef9) will increase coverage by 0.01%.
Report is 2 commits behind head on develop.
The diff coverage is 72.54%.

@@              Coverage Diff              @@
##             develop    #7303      +/-   ##
=============================================
+ Coverage      42.63%   42.65%   +0.01%     
  Complexity      9453     9453              
=============================================
  Files           1151     1151              
  Lines          82669    82699      +30     
  Branches       10771    10776       +5     
=============================================
+ Hits           35246    35275      +29     
+ Misses         43018    43017       -1     
- Partials        4405     4407       +2     

Files Changed	Coverage Δ
...ache/rocketmq/broker/topic/TopicConfigManager.java	56.68% <0.00%> (-0.34%)	⬇️
...mq/client/impl/producer/DefaultMQProducerImpl.java	44.58% <71.42%> (+0.58%)	⬆️
...ocketmq/broker/processor/AdminBrokerProcessor.java	24.37% <92.30%> (+0.30%)	⬆️

... and 17 files with indirect coverage changes

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