TriggerJobOpts: prevent serial execution of trigger jobs

Frank Winklmeierrequested to merge
fwinkl/athena:trig_serial into 24.0

Trigger jobs cannot run in serial mode and always need the AvalancheSchedulerSvc. Add a check to runHLT.py for the athena-based use-case (for athenaHLT there is no serial running anyway).

Also revert !78149 (merged) which was achieving the same but only at runtime rather than configure time.

cc @tamartin

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