feat(schemas): add load_instance=True for Taxref

[bouttier]

N’a probablement aucun impact car le schéma est peu probablement utilisé pour load mais uniquement dump

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.98%. Comparing base (9893f63) to head (28bb902).
Report is 5 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #570      +/-   ##
===========================================
+ Coverage    51.96%   51.98%   +0.01%     
===========================================
  Files           37       37              
  Lines         2417     2418       +1     
===========================================
+ Hits          1256     1257       +1     
  Misses        1161     1161              

Flag	Coverage Δ
pytest	51.98% <100.00%> (+0.01%)	⬆️

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