message: Fix heartbeat settings for deterministic testing
diff: @@ -93,6 +93,8 @@ public:
  fixture(bool autoconn = false)
  : sys(cfg.load<io::middleman, network::test_multiplexer>()
  .set("caf.middleman.enable-automatic-connections", autoconn)
  + .set("caf.middleman.heartbeat-interval", timespan{0})
  + .set("caf.middleman.connection-timeout", timespan{0})
  .set("caf.middleman.workers", size_t{0})
  .set("caf.scheduler.policy", autoconn ? "testing" : "stealing")
  .set("caf.logger.inline-output", true)
  