fix: [cp25]Correct dropped segment num metrics

[XuanYang-cn]

See also: #31891
pr: #37410

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.96%. Comparing base (8ba0a4a) to head (631125b).

Additional details and impacted files

@@           Coverage Diff           @@
##              2.5   #37470   +/-   ##
=======================================
  Coverage   80.95%   80.96%           
=======================================
  Files        1305     1305           
  Lines      182900   182899    -1     
=======================================
+ Hits       148069   148076    +7     
+ Misses      29627    29621    -6     
+ Partials     5204     5202    -2     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	66.94% <ø> (+0.01%)	⬆️
Go	83.24% <100.00%> (+<0.01%)	⬆️

Files with missing lines	Coverage Δ
internal/datacoord/meta.go	89.24% <100.00%> (+0.19%)	⬆️

... and 21 files with indirect coverage changes