typosquat/test_util: Migrate user() fn to diesel-async

[Turbo87]

This was one of the last TestDatabase::connect() users. We should soon be able to remove it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.34%. Comparing base (8e05edd) to head (802c31c).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10055      +/-   ##
==========================================
- Coverage   89.51%   89.34%   -0.17%     
==========================================
  Files         295      295              
  Lines       31215    31275      +60     
==========================================
+ Hits        27943    27944       +1     
- Misses       3272     3331      +59     

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