Fixes for cosmic trigger tests in MC
A couple of fixes for cosmic trigger MC tests (ATR-23207):
- Adding BG3 (EMPTY) to the bunch group set and setting ForceBunchGroupPattern=False for the CTP simulation when running in cosmics mode so that the EMPTY L1 triggers are active.
- Updating the MC art tests to include the doCosmics=True option so that the everything (including the HLT reconstruction) is configured for cosmics.