Use Gradle test fixture support for spring-core

See gh-23550

spring-orm/src/test/java/org/springframework/orm/jpa/AbstractContainerEntityManagerFactoryIntegrationTests.java

@@ -26,9 +26,9 @@ import javax.persistence.Query;
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.orm.jpa.domain.DriversLicense;
 import org.springframework.orm.jpa.domain.Person;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;

spring-orm/src/test/java/org/springframework/orm/jpa/LocalContainerEntityManagerFactoryBeanTests.java

@@ -32,13 +32,13 @@ import javax.persistence.spi.ProviderUtil;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.dao.DataAccessException;
 import org.springframework.dao.OptimisticLockingFailureException;
 import org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver;
 import org.springframework.orm.jpa.persistenceunit.MutablePersistenceUnitInfo;
 import org.springframework.transaction.TransactionStatus;
 import org.springframework.transaction.interceptor.DefaultTransactionAttribute;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;

spring-orm/src/test/java/org/springframework/orm/jpa/support/PersistenceInjectionTests.java

@@ -37,6 +37,7 @@ import org.springframework.beans.factory.FactoryBean;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.test.fixtures.io.SerializationTestUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.orm.jpa.AbstractEntityManagerFactoryBeanTests;
 import org.springframework.orm.jpa.DefaultJpaDialect;
@@ -46,7 +47,6 @@ import org.springframework.stereotype.Repository;
 import org.springframework.tests.context.SimpleMapScope;
 import org.springframework.tests.mock.jndi.ExpectedLookupTemplate;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
-import org.springframework.util.SerializationTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;