Use Gradle test fixture support for spring-core

See gh-23550

spring-tx/src/test/java/org/springframework/transaction/annotation/AnnotationTransactionAttributeSourceTests.java

@@ -31,13 +31,13 @@ import org.junit.jupiter.api.Test;
 import org.springframework.aop.framework.Advised;
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.tests.transaction.CallCountingTransactionManager;
 import org.springframework.transaction.interceptor.NoRollbackRuleAttribute;
 import org.springframework.transaction.interceptor.RollbackRuleAttribute;
 import org.springframework.transaction.interceptor.RuleBasedTransactionAttribute;
 import org.springframework.transaction.interceptor.TransactionAttribute;
 import org.springframework.transaction.interceptor.TransactionInterceptor;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 

spring-tx/src/test/java/org/springframework/transaction/config/AnnotationDrivenTests.java

@@ -27,9 +27,9 @@ import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.support.ClassPathXmlApplicationContext;
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.tests.transaction.CallCountingTransactionManager;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 

spring-tx/src/test/java/org/springframework/transaction/interceptor/TransactionAttributeSourceAdvisorTests.java

@@ -20,7 +20,7 @@ import java.util.Properties;
 
 import org.junit.jupiter.api.Test;
 
-import org.springframework.util.SerializationTestUtils;
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 
 /**
  * @author Rod Johnson

spring-tx/src/test/java/org/springframework/transaction/interceptor/TransactionInterceptorTests.java

@@ -24,13 +24,13 @@ import org.junit.jupiter.api.Test;
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.transaction.PlatformTransactionManager;
 import org.springframework.transaction.TransactionDefinition;
 import org.springframework.transaction.TransactionException;
 import org.springframework.transaction.TransactionManager;
 import org.springframework.transaction.TransactionStatus;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;

spring-tx/src/test/java/org/springframework/transaction/support/JtaTransactionManagerSerializationTests.java

@@ -21,9 +21,9 @@ import javax.transaction.UserTransaction;
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.tests.mock.jndi.SimpleNamingContextBuilder;
 import org.springframework.transaction.jta.JtaTransactionManager;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;