loosen too tight dependendency on cython version

Index: pyproject.toml
--- pyproject.toml.orig
+++ pyproject.toml
@@ -1,7 +1,7 @@
 [build-system]
 requires = ["setuptools",
             "setuptools_scm>=6.2",
-            "cython==0.29.36",
+            "cython>=0.29.36",
             "numpy>=1.25,<2",
             "extension-helpers"]
 build-backend = 'setuptools.build_meta'
