Issue #19437: Fix error handling of CDataType_from_buffer()

KeepRef() decreases the reference counter of its 'keep' parameter on error

Modules/_ctypes/_ctypes.c

@@ -454,7 +454,6 @@ CDataType_from_buffer(PyObject *type, PyObject *args)
 
     Py_INCREF(obj);
     if (-1 == KeepRef((CDataObject *)result, -1, obj)) {
-        Py_DECREF(result);
         return NULL;
     }
     return result;