[#3043] Reduce Sentry noise by downgrading expected exceptions as warnings

[pi-sigma]

Taiga: https://taiga.maykinmedia.nl/project/open-inwoner/us/3043?no-milestone=1

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 94.20%. Comparing base (eaf6816) to head (b03abd6).

Files with missing lines	Patch %	Lines
src/open_inwoner/accounts/signals.py	50.00%	1 Missing ⚠️
src/open_inwoner/openzaak/api_models.py	0.00%	1 Missing ⚠️
src/open_inwoner/openzaak/clients.py	0.00%	1 Missing ⚠️
src/open_inwoner/openzaak/notifications.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1634      +/-   ##
===========================================
- Coverage    94.20%   94.20%   -0.01%     
===========================================
  Files         1083     1083              
  Lines        39955    39956       +1     
===========================================
  Hits         37641    37641              
- Misses        2314     2315       +1     

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