DerivationFrameworkLLP: Fix clang15 compilation error
Fix clang15 compilation with error: chosen constructor is explicit in copy-initialization
- see e.g. https://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/MASTERWebArea/ardoc_web_areamaster64BC7AthenaOpt/ARDOC_Log_2023-03-22T2101/PhysicsAnalysis_DerivationFramework_DerivationFrameworkLLP.html
Tagging @galbouy for info.