Merged requested to merge jchapman/athena:FixATLASSIM-6423_main into master
Previously this function had no protection, now protection has been added following the conventions in ROOT 6.26.6:
It should be noted that CLHEP uses a different convention: https://gitlab.cern.ch/CLHEP/CLHEP/-/blob/develop/Vector/src/ThreeVector.cc#L58-64
This should fix ATLASSIM-6423.
The change does not seem to alter the output of the CI tests, so marking it as ready.
Thanks to @christos for the discussions.