Fix T85573: Building with Python 3.10a5 fails

Replace deprecated _PyUnicode_AsString{AndSize} usage.

T83626 still needs to be resolved before 3.10 is usable.

source/blender/freestyle/intern/python/BPy_SShape.cpp

@@ -201,7 +201,7 @@ static int SShape_name_set(BPy_SShape *self, PyObject *value, void *UNUSED(closu
     PyErr_SetString(PyExc_TypeError, "value must be a string");
     return -1;
   }
-  const char *name = _PyUnicode_AsString(value);
+  const char *name = PyUnicode_AsUTF8(value);
   self->ss->setName(name);
   return 0;
 }