fix: [2.5] Remove frequently updating metric to avoid mutex contention

[bigsheeper]

issue: #37630

Reduce the frequency of updateIndexTasksMetrics to avoid holding the mutex for long periods.

pr: #38775

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.45%. Comparing base (6fa096e) to head (be00199).

❗ There is a different number of reports uploaded between BASE (6fa096e) and HEAD (be00199). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (6fa096e)	HEAD (be00199)
	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##              2.5   #38778       +/-   ##
===========================================
- Coverage   81.05%   69.45%   -11.61%     
===========================================
  Files        1383      294     -1089     
  Lines      195503    26419   -169084     
===========================================
- Hits       158472    18349   -140123     
+ Misses      31457     8070    -23387     
+ Partials     5574        0     -5574     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	69.45% <ø> (-0.02%)	⬇️
Go	∅ <ø> (∅)

see 1090 files with indirect coverage changes

[sre-ci-robot]

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[mergify]

@bigsheeper cpp-unit-test check failed, comment rerun cpp-unit-test can trigger the job again.