Replace _PyUnicode_AsString with PyUnicode_AsUTF8

Author: Avasam

win32/src/PyWinTypes.h

@@ -52,12 +52,8 @@
 // Macro to handle PyObject layout changes in Py3k
 #define PYWIN_OBJECT_HEAD PyVarObject_HEAD_INIT(NULL, 0)
 
-/* Attribute names are passed as Unicode in Py3k, so use a macro to
-    switch between string and unicode conversion.  This function is not
-    documented, but is used extensively in the Python codebase itself,
-    so it's reasonable to assume it won't disappear anytime soon.
-*/
-#define PYWIN_ATTR_CONVERT (char *)_PyUnicode_AsString
+// This macro is kept for legacy reason as it's casting from `const char *` to `char *`
+#define PYWIN_ATTR_CONVERT (char *)PyUnicode_AsUTF8
 
 typedef Py_ssize_t Py_hash_t;