Make some python codes HepMC3 compatible (small MR)

In this MR:

• Make some python codes HepMC3 compatible

This merge request affects 2 packages:

• Generators/GeneratorModules
• Generators/ParticleGun

Affected files list will not be printed in this case

added Generators master review-pending-level-1 labels

changed title from Make some python codes HePMC3 compatible to Make some python codes HepMC3 compatible (small MR)

CI Result SUCCESS (hash 4a694059)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis	DetCommon
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
DetCommon: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 30225]

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

merged

mentioned in commit 6ddadff9

added sweep:ignore label