fix: [2.5] Fix task delta cache data race

[bigsheeper]

issue: #40258

pr: #40259

[weiliu1031]

/lgtm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.89%. Comparing base (82c000a) to head (b0f0c75).
Report is 2 commits behind head on 2.5.

Additional details and impacted files

@@             Coverage Diff             @@
##              2.5   #40262       +/-   ##
===========================================
+ Coverage   70.15%   80.89%   +10.74%     
===========================================
  Files         304     1418     +1114     
  Lines       28274   200212   +171938     
===========================================
+ Hits        19835   161962   +142127     
- Misses       8439    32570    +24131     
- Partials        0     5680     +5680     

Components	Coverage Δ
Client	79.28% <ø> (∅)
Core	70.15% <ø> (ø)
Go	82.80% <100.00%> (∅)

Files with missing lines	Coverage Δ
internal/querycoordv2/task/scheduler.go	87.31% <100.00%> (ø)

... and 1113 files with indirect coverage changes

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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