limit sdist contents

[samuelcolvin]

see PyO3/maturin#1153 and pydantic/pydantic#4542

[codecov-commenter]

Codecov Report

Merging #257 (f42d469) into main (feac27e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #257   +/-   ##
=======================================
  Coverage   98.60%   98.60%           
=======================================
  Files          51       51           
  Lines        5226     5227    +1     
  Branches       37       37           
=======================================
+ Hits         5153     5154    +1     
  Misses         73       73           

Impacted Files	Coverage Δ
src/lib.rs	100.00% <100.00%> (ø)

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