log member attribute changes

We do not expect these, but prudent to log.

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/discovery/HazelcastCoreTopologyService.java

@@ -288,6 +288,7 @@ public void memberRemoved( MembershipEvent membershipEvent )
         @Override
         public void memberAttributeChanged( MemberAttributeEvent memberAttributeEvent )
         {
+            log.info( "Core member attribute changed %s", memberAttributeEvent );
         }
     }
 }