Reinstate @DirtiesContext on shutdown endpoint test

Closes gh-10548

spring-boot-samples/spring-boot-sample-actuator/src/test/java/sample/actuator/ShutdownSampleActuatorApplicationTests.java

@@ -27,6 +27,7 @@ import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
 import org.springframework.boot.test.web.client.TestRestTemplate;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.junit4.SpringRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -55,6 +56,7 @@ public class ShutdownSampleActuatorApplicationTests {
 	}
 
 	@Test
+	@DirtiesContext
 	public void testShutdown() throws Exception {
 		@SuppressWarnings("rawtypes")
 		ResponseEntity<Map> entity = this.restTemplate