Use the thread safe slimCopy in EMBremCollectionBuilder

Since we do not set up m_setPersistificationHints to true anyhow

https://gitlab.cern.ch/atlas/athena/blob/2485766e28e9f1a9cb5c3661b4c873c4a9550ec5/Tracking/TrkTools/TrkTrackSlimmingTool/TrkTrackSlimmingTool/TrackSlimmingTool.h

We can use avoid the thread unsafe interface .

changed the description

This merge request affects 1 package:

• Reconstruction/egamma/egammaAlgs

added Egamma Reconstruction master review-pending-level-1 labels

CI Result SUCCESS (hash 95029be4)

	Athena	AthSimulation
externals
cmake
make
required tests
optional tests

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Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 4817]

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

merged

mentioned in commit 7364791b

added sweep:ignore label