Merge branch 'py312.RootUtils-20240523' into 'main'

RootUtils: Update for python 3.12.

See merge request !71649

Control/RootUtils/src/pyroot/PyROOTPickle.cxx

 /*
-  Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 */
 
 /**
@@ -95,7 +95,7 @@ PyObject* CPPInstanceExpand( PyObject*, PyObject* args )
   // use the PyString macros to by-pass error checking; do not adopt the buffer,
   // as the local TBufferFile can go out of scope (there is no copying)
   TBufferFile buf( TBuffer::kRead,
-                   PyUnicode_GET_SIZE( pybuf ),
+                   PyUnicode_GET_LENGTH( pybuf ),
                    (char*)PyGetString( pybuf ).first.c_str(),
                    kFALSE );