Downgrade Cython version to 3.0.12

Author: maxbachmann

.github/workflows/releasebuild.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install pytest hypothesis pandas mypy Cython==3.1.3
+          pip install pytest hypothesis pandas mypy Cython==3.0.12
 
       # The cythonized files allow installation from the sdist without cython
       - name: Generate cython