Try pg8000 on Appveyor 3.12

setup.py

@@ -236,6 +236,8 @@ def read_file(*path):
             # 2.7.6+ is needed for PostgreSQL 11;
             # 2.8 is needed for conn.info
             'psycopg2 >= 2.8.3',
+            # psycopg2 isn't importing on Appveyor/3.12b4.
+            'pg8000; python_version == "3.12" and sys_platform == "win32"',
         ],
         'postgresql: platform_python_implementation == "PyPy"': [
             # 2.8.0+ is needed for Python 3.7

src/relstorage/tests/reltestbase.py

@@ -317,7 +317,7 @@ def _make_readonly(self):
         # checkWriteMethods in ReadOnlyStorage assumes that
         # the object has an undo() method, even though that's only
         # required if it's IStorageUndoable, aka history-preserving.
-        super()._make_readonly()
+        super()._make_readonly() # pylint:disable=no-member
         storage = self._storage
         if not hasattr(storage, 'undo'):
             def undo(*args, **kwargs):