TriggerTest: Run MC grid tests with 4 threads
Run the MC grid tests which use the full Dev, Physics, PhysicsP1 and MC menus with 4 threads instead of 1 to make them faster. This should help with test timeouts, ATR-20466.
Tests updated:
- test_trig_mc_v1Dev_grid.py
- test_trig_mc_v1Dev_pu80_grid.py
- test_trig_mc_v1Dev_writeBS_grid.py
- test_trig_mc_v1MC_grid.py
- test_trig_mc_v1PhysP1_grid.py
- test_trig_mc_v1Phys_grid.py