Updates test_priorities for BGS strategy
Updates test_priorities for BGS strategy

- Updated test for 'done is done regardless of ZWARN' to use ELGs rather
  than BGS targets.
- BGS does not use 'DONE' in standard operation, only 'MORE_ZGOOD'
- Added test for BGS MORE_ZGOOD ranking below MWS

desihub/desitarget,desihub/desitarget