Bump minimum required Cython version (#799)

0.29.24 is needed to compile properly under Python 3.10

Author: elprans

setup.py

@@ -25,7 +25,7 @@
 from setuptools.command import build_ext as setuptools_build_ext
 
 
-CYTHON_DEPENDENCY = 'Cython(>=0.29.20,<0.30.0)'
+CYTHON_DEPENDENCY = 'Cython(>=0.29.24,<0.30.0)'
 
 # Minimal dependencies required to test asyncpg.
 TEST_DEPENDENCIES = [