Reverting as this is just a test

This test has unusual structure.
If we want to remove `synchronized`, we should be able to rewrite the test without using `synchronized` like other tests.

Author: harawata

src/test/java/org/apache/ibatis/submitted/primitive_result_type/IbatisConfig.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.
@@ -21,27 +21,24 @@
 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
-import org.apache.ibatis.util.LockKit;
 
 public class IbatisConfig {
-  private static final LockKit.ComputedOnce computedOnce = new LockKit.ComputedOnce();
+
   private static SqlSessionFactory sqlSessionFactory;
 
   private IbatisConfig() {
   }
 
-  private static void init() {
-    computedOnce.runOnce(() -> {
-      if (sqlSessionFactory == null) {
-        try {
-          final String resource = "org/apache/ibatis/submitted/primitive_result_type/ibatis.xml";
-          Reader reader = Resources.getResourceAsReader(resource);
-          sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
-        } catch (Exception e) {
-          throw new RuntimeException(e);
-        }
+  private static synchronized void init() {
+    if (sqlSessionFactory == null) {
+      try {
+        final String resource = "org/apache/ibatis/submitted/primitive_result_type/ibatis.xml";
+        Reader reader = Resources.getResourceAsReader(resource);
+        sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
+      } catch (Exception e) {
+        throw new RuntimeException(e);
       }
-    });
+    }
   }
 
   public static SqlSession getSession() {