fix: [2.4] Set the start time for index tasks that no need actual building

[xiaocai2333]

issue: #38354

[mergify]

@xiaocai2333 Please associate the related pr of master to the body of your Pull Request. (eg. “pr: #”)

[mergify]

@xiaocai2333 Please associate the related issue to the body of your Pull Request. (eg. “issue: #”)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.31%. Comparing base (c4b6460) to head (e998b26).
Report is 8 commits behind head on 2.4.

Additional details and impacted files

@@             Coverage Diff             @@
##              2.4   #38353       +/-   ##
===========================================
- Coverage   80.41%   70.31%   -10.10%     
===========================================
  Files        1074     1074               
  Lines      168774   168775        +1     
===========================================
- Hits       135713   118672    -17041     
- Misses      28613    45656    +17043     
+ Partials     4448     4447        -1     

Files with missing lines	Coverage Δ
internal/datacoord/task_index.go	84.67% <100.00%> (+0.05%)	⬆️

... and 274 files with indirect coverage changes

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: czs007, xiaocai2333

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• internal/datacoord/OWNERS [czs007]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment