Add test for 'group_dy' without 'partition_by'

[dreadatour]

Follow-up for the #649

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.66%. Comparing base (00e03c8) to head (f46cde3).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #650      +/-   ##
==========================================
+ Coverage   87.64%   87.66%   +0.01%     
==========================================
  Files         111      111              
  Lines       10598    10598              
  Branches     1435     1435              
==========================================
+ Hits         9289     9291       +2     
+ Misses        946      945       -1     
+ Partials      363      362       -1     

Flag	Coverage Δ
datachain	87.61% <ø> (+0.01%)	⬆️

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