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

@@ -67,17 +67,28 @@ 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']
         no-extensions: ['', 'Y']
+        experimental: [false]
         os: [ubuntu, macos, windows]
         exclude:
           - os: macos
             no-extensions: 'Y'
           - os: windows
             no-extensions: 'Y'
+        include:
+          - pyver: 3.12-dev
+            no-extensions: ''
+            experimental: true
+            os: ubuntu
+          - pyver: 3.12-dev
+            no-extensions: 'Y'
+            experimental: true
+            os: ubuntu
       fail-fast: false
     runs-on: ${{ matrix.os }}-latest
     timeout-minutes: 15
+    continue-on-error: ${{ matrix.experimental }}
     steps:
     - name: Checkout
       uses: actions/checkout@v3

CHANGES/433.misc

@@ -0,0 +1 @@
+Use cython 3.0.0b1 (or newer), fixing Python 3.12 compatibility.

requirements/ci.txt

@@ -1,6 +1,6 @@
 build==0.10.0
 coverage==7.2.2
-cython==0.29.33
+cython==3.0.0b1
 mypy==1.1.1; implementation_name=="cpython"
 pre-commit==3.1.1
 pytest==7.2.2

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]