Fix checkstyle header violation

See gh-24337

Author: philwebb

buildSrc/src/test/java/org/springframework/boot/build/bom/BomPluginIntegrationTests.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.boot.build.bom;
 
 import java.io.File;