I feel like getting notifications about a board's background being
changed isn't very useful information and could interrupt the flow
of other important information such as Card changes or movement,
so I think we should not support this event and
should simply ignore such payloads in the future.
"Local" datetimes are local to the server (or rather, are using
settings.TIME_ZONE), which in most cases is not what the recipient of the
message is expecting.