Most sessions in my experience are not "promoted" by the landlord. "Promoted" usually means someone has arranged the event, booked the performers, etc. In most cases sessions are merely permitted by the landlord and advertised by word of mouth, and more between musicians than potential audience.

If the landlord simply advertises "folk music here tonight" then under the new guidance that should be OK. However if he advertises a named performer then it's regulated entertainment.