fix: lost DroppedAt field when DropCollection

[chyezh]

issue: #33097
pr: #33766

[chyezh]

rerun ut

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.23%. Comparing base (ff9bb17) to head (535a3e8).
Report is 3 commits behind head on 2.4.

Additional details and impacted files

@@           Coverage Diff           @@
##              2.4   #33767   +/-   ##
=======================================
  Coverage   82.22%   82.23%           
=======================================
  Files        1013     1013           
  Lines      129075   129077    +2     
=======================================
+ Hits       106135   106141    +6     
  Misses      18940    18940           
+ Partials     4000     3996    -4     

Files	Coverage Δ
internal/datacoord/meta.go	93.47% <100.00%> (+0.01%)	⬆️

... and 25 files with indirect coverage changes

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chyezh, czs007

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