Fix refs blocking docs build

[sydney-runkle]

WARNING -  griffe: /Users/programming/pydantic_work/pydantic-extra-types/pydantic_extra_types/isbn.py:18: No type or
           annotation for parameter 'value'
WARNING -  griffe: /Users/programming/pydantic_work/pydantic-extra-types/pydantic_extra_types/isbn.py:18: Parameter 'value'
           does not appear in the function signature
WARNING -  griffe: /Users/programming/pydantic_work/pydantic-extra-types/pydantic_extra_types/isbn.py:37: No type or
           annotation for parameter 'value'
WARNING -  griffe: /Users/programming/pydantic_work/pydantic-extra-types/pydantic_extra_types/isbn.py:37: Parameter 'value'
           does not appear in the function signature

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (634487f) 100.00% compared to head (eeee1ba) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #125   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          665       665           
  Branches       166       166           
=========================================
  Hits           665       665           

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