fix: Check partition in current target when observing partition load status (#34282)

[congqixia]

Cherry-pick from master pr: #34282 See also #34234

LoadPartitions does not guarantee the current target has loading partitions if there are some partitions already loaded before.

This PR check current target contains the partition to load when advancing loading percentage to 100.

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: congqixia

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• ~~internal/querycoordv2/checkers/OWNERS~~ [congqixia]
• ~~internal/querycoordv2/meta/OWNERS~~ [congqixia]
• ~~internal/querycoordv2/observers/OWNERS~~ [congqixia]

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.83%. Comparing base (06d9d25) to head (12a3c9e). Report is 17 commits behind head on 2.4.

Additional details and impacted files

@@            Coverage Diff             @@
##              2.4   #34305      +/-   ##
==========================================
- Coverage   81.85%   81.83%   -0.02%     
==========================================
  Files        1015     1015              
  Lines      130621   130622       +1     
==========================================
- Hits       106919   106896      -23     
- Misses      19699    19715      +16     
- Partials     4003     4011       +8     

Files	Coverage Δ
internal/querycoordv2/checkers/balance_checker.go	95.12% <100.00%> (ø)
internal/querycoordv2/checkers/channel_checker.go	84.67% <100.00%> (ø)
internal/querycoordv2/checkers/leader_checker.go	95.23% <100.00%> (ø)
internal/querycoordv2/checkers/segment_checker.go	88.30% <100.00%> (-3.23%)	:arrow_down:
internal/querycoordv2/meta/target.go	95.45% <100.00%> (+0.16%)	:arrow_up:
internal/querycoordv2/meta/target_manager.go	88.29% <100.00%> (+0.15%)	:arrow_up:
...rnal/querycoordv2/observers/collection_observer.go	88.20% <100.00%> (ø)
internal/querycoordv2/observers/target_observer.go	79.44% <100.00%> (ø)

... and 31 files with indirect coverage changes

[weiliu1031]

/lgtm