Apply fix from pybind#1494

Author: lopuhin

include/pybind11/detail/class.h

@@ -441,7 +441,8 @@ extern "C" inline int pybind11_clear(PyObject *self) {
 /// Give instances of this type a `__dict__` and opt into garbage collection.
 inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
     auto type = &heap_type->ht_type;
-#if defined(PYPY_VERSION)
+// https://github.com/pybind/pybind11/pull/1494
+#if defined(PYPY_VERSION) && (PYPY_VERSION_NUM < 0x06000000)
     pybind11_fail(std::string(type->tp_name) + ": dynamic attributes are "
                                                "currently not supported in "
                                                "conjunction with PyPy!");