`notes_with_associations` are used for `participant` declarations, but `Participable`
only really cares about the target entity project, and not the participants
projects.
`notes_with_associations` are also used in `Commit::has_been_reverted?` which
employs the reference extractor of the commit, so no references to the notes
projects are made there (`Mentionable::all_references` cares only about the
`author` and other `attr_mentionable`). A paralel situation occurs on
`Issue::referenced_merge_requests`.
