fix: Fix order observability of group-by-dyn

[ritchie46]

No description provided.

[github-actions]

The uncompressed lib size after this PR is 1118.1165 MB.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.00%. Comparing base (92fd75d) to head (b80c167).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rates/polars-plan/src/plans/optimizer/set_order.rs	60.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #20615   +/-   ##
=======================================
  Coverage   79.00%   79.00%           
=======================================
  Files        1566     1566           
  Lines      221034   221034           
  Branches     2510     2510           
=======================================
+ Hits       174618   174620    +2     
+ Misses      45842    45840    -2     
  Partials      574      574           

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