Fixing loading of param card file on grid jobs for DSIDs 600776-9

Description of bug

Jobs are failing on the grid for JOs with dsids 600776-9. This is due to ill accessing of param_card file which works when running locally but it does not work on the grid.

Changes introduced

Fixing 600xxx/600776/PowhegControl_ttFCNC_NLO.py

Tests

Jobs are running fine locally. Grid jobs not tested.

Issues resolved

Fixing failing jobs in ATLMCPROD-9162