Fix test server merge

Author: Sushisource

temporal-test-server/src/main/java/io/temporal/internal/testservice/StateMachines.java

@@ -2563,9 +2563,17 @@ static Priority mergePriorities(Priority parent, Priority child) {
     }
     Priority.Builder result = Priority.newBuilder();
     result.setPriorityKey(parent.getPriorityKey());
+    result.setFairnessKey(child.getFairnessKey());
+    result.setFairnessWeight(child.getFairnessWeight());
     if (child.getPriorityKey() != 0) {
       result.setPriorityKey(child.getPriorityKey());
     }
+    if (!child.getFairnessKey().isEmpty()) {
+      result.setFairnessKey(child.getFairnessKey());
+    }
+    if (child.getFairnessWeight() != 0) {
+      result.setFairnessWeight(child.getFairnessWeight());
+    }
     return result.build();
   }
 }