fix: Don't merge Enum categories on append

[coastalwhite]

Fixes #22764.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.99%. Comparing base (3a7e226) to head (ec5e943).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22765      +/-   ##
==========================================
+ Coverage   80.98%   80.99%   +0.01%     
==========================================
  Files        1672     1672              
  Lines      236490   236487       -3     
  Branches     2791     2787       -4     
==========================================
+ Hits       191519   191547      +28     
+ Misses      44303    44274      -29     
+ Partials      668      666       -2     

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