bpo-39573: Clean up modules and headers to use Py_IS_TYPE() function (GH-18521)

diff --git a/Modules/_gdbmmodule.c b/Modules/_gdbmmodule.c
index a815819..7a9649b 100644
--- a/Modules/_gdbmmodule.c
+++ b/Modules/_gdbmmodule.c
@@ -44,7 +44,7 @@
 
 #include "clinic/_gdbmmodule.c.h"
 
-#define is_dbmobject(v) (Py_TYPE(v) == &Dbmtype)
+#define is_dbmobject(v) Py_IS_TYPE(v, &Dbmtype)
 #define check_dbmobject_open(v) if ((v)->di_dbm == NULL) \
     { PyErr_SetString(DbmError, "GDBM object has already been closed"); \
       return NULL; }