Fix checkstyle header violations

See gh-24337

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/SpringBootTestRandomPortEnvironmentPostProcessor.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.boot.test.web;
 
 import java.util.Objects;

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/system/OutputExtensionExtendWithTests.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.boot.test.system;
 
 import org.junit.jupiter.api.Test;

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/SpringBootTestRandomPortEnvironmentPostProcessorTests.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.boot.test.web;
 
 import java.util.Collections;

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/client/scan/SimpleFactoryBean.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.boot.test.web.client.scan;
 
 import org.springframework.beans.factory.FactoryBean;