Upgrade cython to 3.0.0b1, add 3.12 to test matrix

This release is compatible with Python 3.12a05 (and up).  While here, extend
the tox configuration to also cover 3.11 and 3.12, and have GitHub test against
3.12.

.github/workflows/ci.yml

@@ -67,7 +67,7 @@ jobs:
     needs: [lint]
     strategy:
       matrix:
-        pyver: ['3.8', '3.9', '3.10', '~3.11.0-0']
+        pyver: ['3.8', '3.9', '3.10', '3.11', '3.12']
         no-extensions: ['', 'Y']
         os: [ubuntu, macos, windows]
         exclude:

requirements/ci.txt

@@ -1,6 +1,6 @@
 build==0.10.0
 coverage==7.2.1
-cython==0.29.33
+cython==3.0.0b1
 mypy==1.0.1; implementation_name=="cpython"
 pre-commit==3.1.1
 pytest==7.2.1

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 
-envlist = check, clean, {py38,py39,py310}-{cython,pure}, report
+envlist = check, clean, {py38,py39,py310,py311,py312}-{cython,pure}, report
 
 [testenv]