Have to disable ubuntu/3.12 because persistent won't build with asser…

…tions enabled.

.github/workflows/tests.yml

@@ -92,6 +92,12 @@ jobs:
         exclude:
           - os: macos-latest
             python-version: pypy-3.9
+          # Can't build persistent on 3.12 with -UNDEBUG because it
+          # accesses fields of objects that aren't there in assert statements;
+          # we build linux with assertions enabled, and there is no 3.12
+          # persistent wheel yet, so we have to exclude that one.
+          - os: ubuntu-latest
+            python-version: "3.12-dev"
 
     steps:
       - name: checkout

pyproject.toml

@@ -15,11 +15,16 @@ requires = [
      # 3.0 in general has improved language support.
      # Python 3.12 requires a snapshot at this writing (2023-06-29). This is just before
      # 3.0rc1
+     # "Cython @ https://github.com/cython/cython/archive/37f4dcdc04547875e2836fda076f5707ec50e579.zip",
      # Unfortunately, markers like python_version do not work for remote installs,
-     # so we may always get that one?
-     # Remember to change this in tests.yml as well
-     "Cython @ https://github.com/cython/cython/archive/37f4dcdc04547875e2836fda076f5707ec50e579.zip",
-     "Cython >= 3.0b3; python_version < '3.12'",
+     # so we always install that, even if we then provide a different requirement where
+     # markers DO work. This is a problem beacuse the snapshot cannot be compiled on Appveyor.
+     # That's OK, because our tests.yml and make-manylinux install this stuff manually where markers
+     # DO work. It just means that we cannot be built from a sdist on Python 3.12 without
+     # --no-build-isolation or using setup.py directly; but as soon as the Cython version is released,
+     # we can be.
+
+     "Cython >= 3.0b3",
      # cffi on py3.12 macOS at least fails to install from its wheel if we let it get installed
      # as part of persistent:
      # OSError: [Errno 66] Directory not empty: '///persistent.../.eggs/cffi-1.15.1-py3.12-macosx-10.9-universal2.egg/cffi-1.15.1.dist-info' -> '//persistent_/.eggs/cffi-1.15.1-py3.12-macosx-10.9-universal2.egg/EGG-INFO'