TrkTrackCollectionMerger: ToolHandle constness fix.
Make mergeTrack() non-const, to avoid calling a non-const method through a const ToolHandle.
GitLab jobs artifacts no longer stored forever as of Monday, November 4th 08:30h. Further information under https://cern.ch/otg0152576
Make mergeTrack() non-const, to avoid calling a non-const method through a const ToolHandle.