message: Change IsMappingHelper to IsNestCompatibleMappingHelper
diff: @@ -213,9 +213,9 @@ int IsInstanceOfRegisteredType(PyObject* obj, const char* type_name) {
  // Returns 1 if `o` is considered a mapping for the purposes of Flatten().
  // Returns 0 otherwise.
  // Returns -1 if an error occurred.
  -int IsMappingHelper(PyObject* o) {
  +int IsNestCompatibleMappingHelper(PyObject* o) {
  static auto* const check_cache = new CachedTypeCheck([](PyObject* to_check) {
  - return IsInstanceOfRegisteredType(to_check, "Mapping");
  + return IsInstanceOfRegisteredType(to_check, "MutableMapping");
  });
  if (PyDict_Check(o)) return true;
  return check_cache->CachedLookup(o);
  