For zero-downtime deployed in a mixed code environment between 12.2 and
12.3, the branch and tag name cache is incorrectly invalidated - a push
to an old machine will not clear the redis set version of the cache on
the new machine.

This commit ensures that, in 12.3, both set and non-set versions of the
cache are invalidated, but does not write or consult the set version of
the cache. . In 12.4, it will be safe to switch branch and tag names to
the redis set cache both it and the legacy cache will be invalidated
appropriately in such a mixed code environment.

This delays the full implementation of the feature by one release, but
in the absence of a credible feature-flagging strategy, and amidst an
abundance of caution about the effects of too-eager cache expiration, I
believe this is the best approach available to us.