Correct grouping of custom buildpacks

This commit corrects the order.toml file that is generated and added
to the builder when building an image using custom buildpacks with the
Maven or Gradle plugin in order to support buildpacks that depend on
detection as a group.

Fixes gh-25378

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

@@ -203,7 +203,7 @@ class BootBuildImageIntegrationTests {
 	}
 
 	@TestTemplate
-	void buildsImageWithBuildpackFromImage() throws IOException {
+	void buildsImageWithBuildpacksFromImages() throws IOException {
 		writeMainClass();
 		writeLongNameResource();
 		BuildResult result = this.gradleBuild.build("bootBuildImage", "--pullPolicy=IF_NOT_PRESENT");