This addresses an issue that arises when the owner of a path is the
group under which the project lives (such as `@gitlab-org` for the
Gitlab project..) Gitlab::CodeOwners::GroupsLoader did not add that
group to the list of groups when attempting to determine ownership. This
list of groups is expanded into a list of users that the user
attempting the action (typically a merge) is compared to. Sinc the
project's group is not added to the group list, its members are not
expanded and are thus missing from the list of owners for a given path.