Fix metrics_SUITE connection_metrics flake

Author: dcorbacho

deps/rabbit/test/metrics_SUITE.erl

@@ -204,12 +204,7 @@ queue_metric_idemp(Config, {N, R}) ->
 
 connection_metric_count(Config, Ops) ->
     add_rem_counter(Config, Ops,
-                    {fun(Config) ->
-                             case rabbit_ct_client_helpers:open_unmanaged_connection(Config) of
-                                 {error, _} = E -> throw(E);
-                                 Conn -> Conn
-                             end
-                     end,
+                    {fun rabbit_ct_client_helpers:open_unmanaged_connection/1 end,
                      fun(Cfg) ->
                              rabbit_ct_client_helpers:close_connection(Cfg)
                      end},