Restrict cython to <3.0 (#8337)

pyproject.toml

@@ -1,7 +1,7 @@
 [build-system]
 requires = [
     "setuptools",
-    "cython>=0.25",
+    "cython>=0.25,<3.0",
     "cymem>=2.0.2,<2.1.0",
     "preshed>=3.0.2,<3.1.0",
     "murmurhash>=0.28.0,<1.1.0",

requirements.txt

@@ -22,7 +22,7 @@ setuptools
 packaging>=20.0
 typing_extensions>=3.7.4.1,<4.0.0.0; python_version < "3.8"
 # Development dependencies
-cython>=0.25
+cython>=0.25,<3.0
 pytest>=5.2.0
 pytest-timeout>=1.3.0,<2.0.0
 mock>=2.0.0,<3.0.0

setup.cfg

@@ -31,7 +31,7 @@ zip_safe = false
 include_package_data = true
 python_requires = >=3.6
 setup_requires =
-    cython>=0.25
+    cython>=0.25,<3.0
     numpy>=1.15.0
     # We also need our Cython packages here to compile against
     cymem>=2.0.2,<2.1.0