Fixes of HepMC3 nightlies (small MR)

In this MR:

• fix the compilation of EvtGen in HepMC3 branch

changed title from Fixes of HepMC3 nightlies to Fixes of HepMC3 nightlies (small MR)

This merge request affects 1 package:

• Generators/EvtGen_i

This merge request affects 1 file:

• Generators/EvtGen_i/CMakeLists.txt

added Generators master review-pending-level-1 labels

CI Result SUCCESS (hash a00f3190)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthAnalysis: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 29064]

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 9dd794d5

added sweep:ignore label