[hotfix] Fix shard detector rewatch always returns closed channel (#23734)

[congqixia]

Related to #23637 /kind bug

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[codecov[bot]]

Codecov Report

Merging #23785 (3de1548) into hotfix-2.2.6 (a078e40) will increase coverage by 0.01%. The diff coverage is 62.50%.

@@               Coverage Diff                @@
##           hotfix-2.2.6   #23785      +/-   ##
================================================
+ Coverage         81.44%   81.45%   +0.01%     
================================================
  Files               709      709              
  Lines            100370   100369       -1     
================================================
+ Hits              81746    81758      +12     
+ Misses            15447    15424      -23     
- Partials           3177     3187      +10     

Impacted Files	Coverage Δ
internal/querynode/shard_segment_detector.go	71.85% <57.14%> (+5.38%)	:arrow_up:
internal/querynode/shard_node_detector.go	74.88% <100.00%> (+4.27%)	:arrow_up:

... and 17 files with indirect coverage changes