fix autodetect dynamic attrs in 3.11

Author: Skylion007

include/pybind11/attr.h

@@ -345,9 +345,10 @@ struct type_record {
 
         bases.append((PyObject *) base_info->type);
 
-        if (base_info->type->tp_dictoffset != 0) {
-            dynamic_attr = true;
-        }
+        dynamic_attr |= base_info->type->tp_dictoffset != 0;
+#if PY_VERSION_HEX >= 0x030B0000
+        dynamic_attr |= (base_info->type->tp_flags & Py_TPFLAGS_MANAGED_DICT) != 0;
+#endif
 
         if (caster) {
             base_info->implicit_casts.emplace_back(type, caster);

tests/test_multiple_inheritance.cpp

@@ -230,10 +230,8 @@ TEST_SUBMODULE(multiple_inheritance, m) {
     struct VanillaDictMix1 : Vanilla, WithDict {};
     struct VanillaDictMix2 : WithDict, Vanilla {};
     py::class_<WithDict>(m, "WithDict", py::dynamic_attr()).def(py::init<>());
-    py::class_<VanillaDictMix1, Vanilla, WithDict>(m, "VanillaDictMix1", py::dynamic_attr())
-        .def(py::init<>());
-    py::class_<VanillaDictMix2, WithDict, Vanilla>(m, "VanillaDictMix2", py::dynamic_attr())
-        .def(py::init<>());
+    py::class_<VanillaDictMix1, Vanilla, WithDict>(m, "VanillaDictMix1").def(py::init<>());
+    py::class_<VanillaDictMix2, WithDict, Vanilla>(m, "VanillaDictMix2").def(py::init<>());
 
     // test_diamond_inheritance
     // Issue #959: segfault when constructing diamond inheritance instance