Mark a subgroup-related spec as PostgreSQL-only
Mark a subgroup-related spec as PostgreSQL-only

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/34847

dreampet/gitlab,axilleas/gitlabhq,mmkassem/gitlabhq,t-zuehlsdorff/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,jirutka/gitlabhq,iiet/iiet-git,dplarson/gitlabhq,dplarson/gitlabhq,iiet/iiet-git,dplarson/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,t-zuehlsdorff/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,t-zuehlsdorff/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,axilleas/gitlabhq,jirutka/gitlabhq,dplarson/gitlabhq,stoplightio/gitlabhq