athenaHLT: change default DB alias to Run-3

The `TRIGGERDB` alias is deprecated and still points to the Run-2
database. Since athenaHLT does not support Run-2 configurations we can
change the default to the Run-3 database. Re-running the HLT on a data
file then simply becomes:
athenaHLT -b -f
1 job for athhlt_db in 0 seconds (queued for 61 minutes and 47 seconds)