Correct specialty on a group-location specialty record

Replaces the specialty identifier on a practitioner specialty association at the group-location level. This is a data-correction operation — it does not trigger termination events or lifecycle changes. Use it when the wrong specialty was linked at the group-location level and needs correcting without triggering a termination cycle; for the more specific group-location-network level, use PATCH /practitioners/group-practitioner-location-network-specialties/specialty instead. The specialty association must already exist, and the replacement specialty must be a valid tenant specialty.