python: fix casing for enum variants in stub

[remi-dupre]

Fixes #69

📋 Before Merge Checklist

1. I have chosen a new version number with respect to semver
2. I have updated the version in these files consistently: Cargo.toml, compact-calendar/Cargo.toml, opening-hours-syntax/Cargo.toml, python/Cargo.toml and pyproject.toml
3. I have updated CHANGELOG.md

[codecov]

Codecov Report

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

Project coverage is 85.33%. Comparing base (a08f742) to head (855da9d).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
opening-hours-py/src/types/state.rs	33.33%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #70   +/-   ##
=======================================
  Coverage   85.32%   85.33%           
=======================================
  Files          28       28           
  Lines        2044     2045    +1     
=======================================
+ Hits         1744     1745    +1     
  Misses        300      300           

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