Issue #28147: Fix a memory leak in split-table dictionaries

setattr() must not convert combined table into split table.
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 29a28a7..060a92d 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -249,6 +249,15 @@
 }
 
 
+static PyObject*
+dict_hassplittable(PyObject *self, PyObject *arg)
+{
+    if (!PyArg_Parse(arg, "O!:dict_hassplittable", &PyDict_Type, &arg)) {
+        return NULL;
+    }
+    return PyBool_FromLong(_PyDict_HasSplitTable((PyDictObject*)arg));
+}
+
 /* Issue #4701: Check that PyObject_Hash implicitly calls
  *   PyType_Ready if it hasn't already been called
  */
@@ -3858,6 +3867,7 @@
     {"test_datetime_capi",  test_datetime_capi,              METH_NOARGS},
     {"test_list_api",           (PyCFunction)test_list_api,      METH_NOARGS},
     {"test_dict_iteration",     (PyCFunction)test_dict_iteration,METH_NOARGS},
+    {"dict_hassplittable",      dict_hassplittable,              METH_O},
     {"test_lazy_hash_inheritance",      (PyCFunction)test_lazy_hash_inheritance,METH_NOARGS},
     {"test_long_api",           (PyCFunction)test_long_api,      METH_NOARGS},
     {"test_xincref_doesnt_leak",(PyCFunction)test_xincref_doesnt_leak,      METH_NOARGS},