docs(python): Corrected example result in group_by docs

[rosstitmarsh]

Fix for issue #18168

[MarcoGorelli]

thanks @rosstitmarsh

personally i'd advocate for removing the doctest skips and just adding an extra sort, but that's for a separate discussion, i don't want to block this pr

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.31%. Comparing base (41318c3) to head (0afd613).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18169      +/-   ##
==========================================
- Coverage   80.35%   80.31%   -0.05%     
==========================================
  Files        1496     1498       +2     
  Lines      197825   198632     +807     
  Branches     2822     2822              
==========================================
+ Hits       158966   159528     +562     
- Misses      38337    38582     +245     
  Partials      522      522              

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