Fix unit test failure in PaketoBuilderTests.plainWarApp() caused by container permission issue

Author: LumanSuen

system-test/spring-boot-image-system-tests/src/systemTest/java/org/springframework/boot/image/paketo/PaketoBuilderTests.java

@@ -270,6 +270,9 @@ void plainWarApp() throws Exception {
 		assertThat(result.getOutput()).contains("Running creator");
 		try (GenericContainer<?> container = new GenericContainer<>(imageName)) {
 			container.withExposedPorts(8080);
+			container.withCreateContainerCmdModifier(cmd -> {
+				cmd.withUser("root");
+			});
 			container.waitingFor(Wait.forHttp("/test")).start();
 			ContainerConfig config = container.getContainerInfo().getConfig();
 			ImageAssertions.assertThat(config).buildMetadata((metadata) -> {