fix: rename build backend module to use underscore instead of hyphen

Author: HSiga

pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
 requires = ["setuptools>=42", "setuptools-scm"]
-build-backend = "setuptools-cython"
+build-backend = "setuptools_cython"
 backend-path = ["setuptools-cython"]
 
 [project]