release(2.15.1) : minor fixes

[jacquesfize]

This PR aggregates minor fixes of bugs remaining in the 2.15.0

[codecov]

Codecov Report

Attention: Patch coverage is 70.58824% with 5 lines in your changes missing coverage. Please review.

Project coverage is 83.90%. Comparing base (df951cd) to head (dd6b9c9).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
backend/geonature/core/imports/admin.py	55.55%	4 Missing ⚠️
backend/geonature/core/imports/models.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3293      +/-   ##
===========================================
- Coverage    83.92%   83.90%   -0.02%     
===========================================
  Files          122      122              
  Lines         9691     9699       +8     
===========================================
+ Hits          8133     8138       +5     
- Misses        1558     1561       +3     

Flag	Coverage Δ
pytest	83.90% <70.58%> (-0.02%)	⬇️

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