Fix dependency typo in TruthUtils
As pointed out in the unrelated MR !26305 (merged), cmake complains about not finding FindHepUtils.cmake and this is simply because it should be looking for FindHEPUtils.cmake as far as I can tell.
As pointed out in the unrelated MR !26305 (merged), cmake complains about not finding FindHepUtils.cmake and this is simply because it should be looking for FindHEPUtils.cmake as far as I can tell.