Correct a workaround for PyPy

Author: Cito

src/graphql/pyutils/is_iterable.py

@@ -7,7 +7,7 @@
 collection_types: Any = [Collection]
 if not isinstance({}.values(), Collection):  # Python < 3.7.2
     collection_types.append(ValuesView)
-if not isinstance(array, Collection):  # PyPy issue 3820
+if not issubclass(array, Collection):  # PyPy <= 7.3.9
     collection_types.append(array)
 collection_types = (
     collection_types[0] if len(collection_types) == 1 else tuple(collection_types)