TrigAnalysisTest: Change Trigger configuration in the mc16a test

Changes in the RDOtoRDOTrigger step running in 21.0-mc16a:

• change menu version to v6
• add the run2Config=2016 flag

Discussed in ATR-22237

Trigger/TrigValidation/TrigAnalysisTest/test/test_trigAna_HITtoAOD_trigRel21_mc16a_build.py

@@ -57,8 +57,9 @@ rdo2rdotrig.imf = False
 rdo2rdotrig.explicit_input = True
 rdo2rdotrig.args = '--inputRDOFile=RDO.pool.root --outputRDO_TRIGFile=RDO_TRIG.pool.root'
 rdo2rdotrig.args += ' --asetup="RDOtoRDOTrigger:Athena,21.0-mc16a,slc6,latest"'
-rdo2rdotrig.args += ' --triggerConfig="MCRECO:MC_pp_v7_tight_mc_prescale"'
+rdo2rdotrig.args += ' --triggerConfig="MCRECO:MC_pp_v6_tight_mc_prescale"'
 rdo2rdotrig.args += ' --imf="all:True"'
+rdo2rdotrig.args += ' --preExec="all:from TriggerJobOpts.TriggerFlags import TriggerFlags; TriggerFlags.run2Config=\"2016\""'
 
 # Clear AthFile cache from r21 because it is incompatible with py3 r22 (ATR-21489)
 rm_cache = ExecStep.ExecStep('ClearAthFileCache')