BUG31490101: Fix wrong cast of Python unicode to std::string

This patch replaces the deprecated PyUnicode_GetSize by
PyUnicode_GET_LENGTH.

Author: nmariz

CHANGES.txt

@@ -17,6 +17,7 @@ v8.0.24
 - WL#14027: Add support for Python 3.9
 - BUG#32435181: Add support for Django 3.2
 - BUG#32029891: Add context manager support for pooled connections
+- BUG#31490101: Fix wrong cast of Python unicode to std::string
 
 v8.0.23
 =======

src/mysqlxpb/python.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2020, Oracle and/or its affiliates.
+ * Copyright (c) 2017, 2021, Oracle and/or its affiliates.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License, version 2.0, as
@@ -34,4 +34,4 @@
 #define PyString_CheckExact PyUnicode_CheckExact
 #define PyString_AsString PyUnicode_AsUTF8
 #define PyString_FromString PyUnicode_FromString
-#define PyString_Size PyUnicode_GetSize
+#define PyString_Size PyUnicode_GET_LENGTH