FlavorTagDiscriminants: Fix clang 10 warning.

Spurious copy in range for.

PhysicsAnalysis/JetTagging/FlavorTagDiscriminants/Root/BTagJetAugmenter.cxx

@@ -413,7 +413,7 @@ void BTagJetAugmenter::augment(const xAOD::Jet &jet) {
       max_track_flightDirRelEta = track_flightDirRelEta;
     }
     if (secondary_jf_vtx_index >= 0) {
-      for (const ElementLink<xAOD::TrackParticleContainer> vertex_track_particle : (**m_jf_vertices(btag).at(secondary_jf_vtx_index)).track_links()) {
+      for (const ElementLink<xAOD::TrackParticleContainer>& vertex_track_particle : (**m_jf_vertices(btag).at(secondary_jf_vtx_index)).track_links()) {
         if (*vertex_track_particle == &track_particle) {
           secondaryVtx_track_number++;
           TLorentzVector track_fourVector;