FIX: ensures successive tags can be renamed (PR #12818)

Original bug report: Rename tag not working as expected - bug - Discourse Meta

This bug was caused by the use of oneWay which can be very dangerous in this case, from the documentation:

computed.oneWay only provides an aliased get. The set will not mutate the upstream property, rather causes the current property to become the value set. **This causes the downstream property to permanently diverge from the upstream property.**