tests: Do not use string builder where not needed

underlying jvm will handle this making it easier to read.

Author: hazendaz

src/test/java/org/apache/ibatis/submitted/nestedresulthandler/Item.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2009-2023 the original author or authors.
+ *    Copyright 2009-2024 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -21,7 +21,7 @@ public class Item {
 
   @Override
   public String toString() {
-    return new StringBuilder().append("Item(").append(id).append(", ").append(name).append(" )").toString();
+    return "Item(" + id + ", " + name + " )";
   }
 
   public Integer getId() {

src/test/java/org/apache/ibatis/submitted/nestedresulthandler/Person.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2009-2023 the original author or authors.
+ *    Copyright 2009-2024 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -26,8 +26,7 @@ public class Person {
 
   @Override
   public String toString() {
-    return new StringBuilder().append("Person(").append(id).append(", ").append(name).append(", ").append(items)
-        .append(" )").toString();
+    return "Person(" + id + ", " + name + ", " + items + " )";
   }
 
   public Integer getId() {

src/test/java/org/apache/ibatis/submitted/nestedresulthandler/PersonItemPair.java

@@ -1,5 +1,5 @@
 /*
- *    Copyright 2009-2023 the original author or authors.
+ *    Copyright 2009-2024 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -24,8 +24,7 @@ public class PersonItemPair {
 
   @Override
   public String toString() {
-    return new StringBuilder().append("PersonItemPair(").append(person).append(", ").append(item).append(" )")
-        .toString();
+    return "PersonItemPair(" + person + ", " + item + " )";
   }
 
   public Person getPerson() {