Experiments can be run on high-traffic read-only pages and when a
transaction is initiated, our load balancing code will direct all
queries to the primary.

This update is a no-op most of the time so we skip the update when
we detect that the attributes haven't changed.

ActiveRecord actually already does this under the hood but a
`#transaction` call is still made in the process causing the
undesired behavior with our load balancer.