TaskStatusDB: Test for _task_row_update_statement

[dwhswenson]

I promised more detailed unit tests for this function in #21. Here they are.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.63%. Comparing base (2cffa62) to head (cd63885).
⚠️ Report is 59 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   86.62%   91.63%   +5.00%     
==========================================
  Files           5        5              
  Lines         344      526     +182     
==========================================
+ Hits          298      482     +184     
+ Misses         46       44       -2     

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[dwhswenson]

Putting this on hold (as draft) because I think it might have conflicts with #31. Part of this PR involves actually testing the SQL that gets emitted; this was intended as a way to give a clear picture of what is happening behind the scenes. But the SQL that gets emitted might be dialect-specific.

I'll come back to finish this after #31 is merged in (prefer to get that in and have the conflict block here than the other way around).