Change default for new_generator_mappings to true

Closes gh-7612

spring-boot-samples/spring-boot-sample-jpa/src/test/java/sample/jpa/SampleJpaApplicationTests.java

@@ -22,6 +22,7 @@ import org.junit.runner.RunWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.TestPropertySource;
 import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.test.context.web.WebAppConfiguration;
 import org.springframework.test.web.servlet.MockMvc;
@@ -40,6 +41,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
  */
 @RunWith(SpringRunner.class)
 @SpringBootTest
+@TestPropertySource(properties = "spring.jpa.hibernate.use-new-id-generator-mappings=false")
 @WebAppConfiguration
 public class SampleJpaApplicationTests {