DM-37855: Fix query order_by failure due to inconsistent handling of pkeys.

[TallJimbo]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Base: 85.60% // Head: 85.56% // Decreases project coverage by -0.04% ⚠️

Coverage data is based on head (86c054c) compared to base (6140c9f).
Patch coverage: 95.65% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #778      +/-   ##
==========================================
- Coverage   85.60%   85.56%   -0.04%     
==========================================
  Files         269      269              
  Lines       35359    35279      -80     
  Branches     6025     6026       +1     
==========================================
- Hits        30268    30188      -80     
- Misses       3772     3775       +3     
+ Partials     1319     1316       -3     

Impacted Files	Coverage Δ
tests/test_butler.py	98.18% <ø> (+0.50%)	⬆️
.../butler/registry/queries/expressions/categorize.py	80.00% <93.75%> (+0.45%)	⬆️
python/lsst/daf/butler/registry/tests/_registry.py	98.47% <100.00%> (+<0.01%)	⬆️
python/lsst/daf/butler/formatters/pickle.py	67.85% <0.00%> (-3.58%)	⬇️
python/lsst/daf/butler/datastores/fileDatastore.py	80.89% <0.00%> (-0.54%)	⬇️
python/lsst/daf/butler/core/formatter.py	87.25% <0.00%> (-0.50%)	⬇️

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