BROKER_HEARTBEAT appears to interfere with the celery worker
configuration. If we want to disable or change the heartbeat interval,
It must be from these configuration options.

Just setting --without-heartbeat and/or --heartbeat-interval on the
workers does not fully work. Eg. --without-heartbeat disables sending
heartbeats, but BROKER_HEARTBEAT = 60 means that the connection will get
a 60s heartbeat interval negotiated.