python 3.11 fixes: avoid attrs warning for setting cells

RuntimeWarning: Running interpreter doesn't sufficiently support code object introspection.  Some features like bare super() or accessing __class__ will not work with slotted classes.

Author: asottile

testing/test_assertion.py

@@ -1026,7 +1026,7 @@ def __eq__(self, other):  # pragma: no cover
         assert lines is None
 
     def test_attrs_with_custom_eq(self) -> None:
-        @attr.define
+        @attr.define(slots=False)
         class SimpleDataObject:
             field_a = attr.ib()