Merge branch 'cherry-pick-03c908db-21.0' into '21.0'

Sweeping !24516 from master to 21.0.
Reducing the number of processed files in the egamma pileup ART test

See merge request atlas/athena!24571

Reconstruction/egamma/egammaValidation/test/test_electron_pileup.sh

@@ -4,7 +4,7 @@
 #
 # art-type: grid
 # art-input: mc16_13TeV.423000.ParticleGun_single_electron_egammaET.recon.RDO.e3566_s3113_r10470
-# art-input-nfiles: 30
+# art-input-nfiles: 15
 # art-cores: 4
 # art-include: 21.0/Athena
 # art-include: master/Athena

Reconstruction/egamma/egammaValidation/test/test_gamma_pileup.sh

@@ -4,7 +4,7 @@
 #
 # art-type: grid
 # art-input: mc16_13TeV.423001.ParticleGun_single_photon_egammaET.recon.RDO.e3566_s3113_r10470
-# art-input-nfiles: 30
+# art-input-nfiles: 15
 # art-cores: 4
 # art-include: 21.0/Athena
 # art-include: master/Athena