Fix McParticleUtils compilation in HepMC2-based builds

This fix will only affect the master--HepMC2 nightlies, but merging it here to avoid conflicts.

Tagging @averbyts

added bugfix label

This merge request affects 1 package:

• PhysicsAnalysis/TruthParticleID/McParticleUtils

This merge request affects 1 file:

• PhysicsAnalysis/TruthParticleID/McParticleUtils/src/McVtxFilter.cxx

added 23.0 Analysis review-pending-level-1 labels

The system determined that CI tests (with names matching "^CITest_SimulationRun(2|3)(FullSim|Hit).*$") are not needed for this code change. They are not run. This is not an indicator to restart the job.

CI Result SUCCESS (hash 37a42a16)

	Athena
externals
cmake
make
tests

Full details available on this CI monitor view. Check the JIRA CI status board for known problems
Athena: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 74209]

Minor change. CI is good. Approving. Clara (L1)

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

mentioned in commit 1410613b

merged

mentioned in merge request !64264 (merged)