bpo-39573: Finish converting to new Py_IS_TYPE() macro (GH-18601)

diff --git a/Modules/cjkcodecs/multibytecodec.h b/Modules/cjkcodecs/multibytecodec.h
index 94670ec..4d2b355 100644
--- a/Modules/cjkcodecs/multibytecodec.h
+++ b/Modules/cjkcodecs/multibytecodec.h
@@ -65,7 +65,7 @@
     MultibyteCodec *codec;
 } MultibyteCodecObject;
 
-#define MultibyteCodec_Check(op) (Py_TYPE(op) == &MultibyteCodec_Type)
+#define MultibyteCodec_Check(op) Py_IS_TYPE((op), &MultibyteCodec_Type)
 
 #define _MultibyteStatefulCodec_HEAD            \
     PyObject_HEAD                               \