Make __pydantic_extra__ = None when extra='forbid'

[dmontagu]

This resolves pydantic/pydantic#6332

Here's the pydantic PR adding the relevant test: pydantic/pydantic#6341

[codecov]

Codecov Report

Merging #725 (3473a92) into main (7da65c4) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #725   +/-   ##
=======================================
  Coverage   93.63%   93.63%           
=======================================
  Files          99       99           
  Lines       13911    13911           
  Branches       25       25           
=======================================
  Hits        13026    13026           
  Misses        879      879           
  Partials        6        6           

Impacted Files	Coverage Δ
src/validators/model_fields.rs	98.31% <100.00%> (ø)

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[codspeed-hq]

CodSpeed Performance Report

Merging #725 will not alter performances

_{Comparing pydantic-6332 (3473a92) with main (7da65c4)}

Summary

✅ 125 untouched benchmarks

[jessekrubin]

Oh this is the weird error I was getting!!