fix(auth): avoid crash when get_or_create is not passed with defaults

[nijel]

The compatibility layer introduced in #13640 doesn't gracefully handle when defaults are not passed and leads to crash.

Fixes #14434

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.05%. Comparing base (1a1e3c8) to head (d187896).
Report is 3248 commits behind head on main.

Files with missing lines	Patch %	Lines
weblate/auth/models.py	57.14%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14435      +/-   ##
==========================================
- Coverage   91.05%   91.05%   -0.01%     
==========================================
  Files         614      614              
  Lines       64147    64150       +3     
  Branches     6640     6641       +1     
==========================================
+ Hits        58409    58410       +1     
- Misses       4023     4025       +2     
  Partials     1715     1715              

Files with missing lines	Coverage Δ
weblate/auth/models.py	91.54% <57.14%> (-0.49%)	⬇️

... and 4 files with indirect coverage changes

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