Freeze Cython dep

setup.py

@@ -388,7 +388,7 @@ def run_setup(extensions):
         # 1.) build_ext eats errors at compile time, letting the install complete while producing useful feedback
         # 2.) there could be a case where the python environment has cython installed but the system doesn't have build tools
         if pre_build_check():
-            kw['setup_requires'] = ['Cython>=0.20']
+            kw['setup_requires'] = ['Cython>=0.20,<0.25']
         else:
             sys.stderr.write("Bypassing Cython setup requirement\n")
 

test-requirements.txt

@@ -11,5 +11,5 @@ pure-sasl
 twisted
 gevent>=1.0
 eventlet
-cython>=0.21
+cython>=0.20,<0.25
 packaging