requirements: remove cython restrictions

pyproject.toml

@@ -1,3 +1,3 @@
 [build-system]
-requires = ["setuptools", "pkgconfig", "Cython<3", "setuptools_scm>=1.7"]
+requires = ["setuptools", "pkgconfig", "Cython", "setuptools_scm>=1.7"]
 build-backend = "setuptools.build_meta"

requirements.d/development.txt

@@ -8,7 +8,7 @@ pytest
 pytest-xdist
 pytest-cov
 pytest-benchmark
-Cython <3
+Cython
 twine
 python-dateutil
 pre-commit