LArG4GenShowerLib: enable thread-checker

Remove unnecessary mutable and DataHandle usage.

assigned to @fwinkl

This merge request affects 1 package:

• LArCalorimeter/LArG4/LArG4GenShowerLib

This merge request affects 4 files:

• LArCalorimeter/LArG4/LArG4GenShowerLib/LArG4GenShowerLib/ATLAS_CHECK_THREAD_SAFETY
• LArCalorimeter/LArG4/LArG4GenShowerLib/LArG4GenShowerLib/TestActionShowerLib.h
• LArCalorimeter/LArG4/LArG4GenShowerLib/src/LArG4GenShowerLib.cxx
• LArCalorimeter/LArG4/LArG4GenShowerLib/src/TestActionShowerLib.cxx

Adding @pavol as watcher

added JetEtmiss LAr Simulation master review-pending-level-1 labels

CI Result SUCCESS (hash 9a4f315c)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis	DetCommon
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
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 58185]

Looks good , approving - L1

added review-approved label

removed review-pending-level-1 label

merged

mentioned in commit 850797e8

added sweep:ignore label