test(async): use FakeTime in pooledMap testing

[kt3k]

closes #6287

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.68%. Comparing base (1dee498) to head (8a6fee1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6468   +/-   ##
=======================================
  Coverage   95.68%   95.68%           
=======================================
  Files         576      576           
  Lines       43053    43053           
  Branches     6450     6450           
=======================================
+ Hits        41194    41195    +1     
+ Misses       1820     1819    -1     
  Partials       39       39           

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[satyarohith]

LGTM