Polish access modifiers for test classes

See gh-27736

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/BootBuildImageRegistryIntegrationTests.java

@@ -49,7 +49,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 @GradleCompatibility
 @Testcontainers(disabledWithoutDocker = true)
 @Disabled("Disabled until differences between running locally and in CI can be diagnosed")
-public class BootBuildImageRegistryIntegrationTests {
+class BootBuildImageRegistryIntegrationTests {
 
 	@Container
 	static final RegistryContainer registry = new RegistryContainer().withStartupAttempts(5)

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/DockerSpecTests.java

@@ -32,7 +32,7 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
  * @author Wei Jiang
  * @author Scott Frederick
  */
-public class DockerSpecTests {
+class DockerSpecTests {
 
 	@Test
 	void asDockerConfigurationWithDefaults() {