Update variable beamspot digitisation ART tests

Update variable beamspot digitisation ART tests to have unique outputs so that references would work.

Fixes ATLASSIM-5804.

/cc @bwynne

This merge request affects 1 package:

• Simulation/Tests/DigitizationTests

This merge request affects 2 files:

• Simulation/Tests/DigitizationTests/test/test_Digi_tf_mc21a_presampling_variable.sh
• Simulation/Tests/DigitizationTests/test/test_Digi_tf_mc21a_presampling_variable_TruthOnly.sh

Adding @jchapman as watcher

added Digitization Simulation master review-pending-level-1 labels

CI Result SUCCESS (hash 0cda62bd)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis	DetCommon
externals
cmake
make
required tests
optional 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 51664]

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

merged

mentioned in commit 56ea944d

added sweep:ignore label