worker: Migrate tests suite to async database queries

[Turbo87]

... which allows us to get rid of the flavor = "multi_thread" declaration on the tests :D

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.89%. Comparing base (3fafc87) to head (e8c1b79).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9822      +/-   ##
==========================================
+ Coverage   88.83%   88.89%   +0.06%     
==========================================
  Files         289      289              
  Lines       29852    29868      +16     
==========================================
+ Hits        26519    26552      +33     
+ Misses       3333     3316      -17     

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