Investigate why the Native Build Tools plugin isn't applied in PaketoBuilderTests.nativeApp

[mhalbritter]

spring-boot-system-tests/spring-boot-image-tests/src/systemTest/resources/org/springframework/boot/image/paketo/PaketoBuilderTests-nativeApp.gradle has this snippet:

bootJar {
	manifest {
		attributes(
			'Implementation-Version': '1.0.0',
			'Implementation-Title': 'Paketo Test',
			'Spring-Boot-Native-Processed': 'true'
		)
	}
}

'Spring-Boot-Native-Processed': 'true' shouldn't be necessary, because it is set by our NativeImagePluginAction. However, for reasons unclear to me, the NativeImagePluginAction isn't executed in this build, despite the NBT plugin in the plugins section.

When removing the .withPluginClasspath call in org.springframework.boot.testsupport.gradle.testkit.GradleBuild#prepareRunner, it works. No idea if that is a red herring or not.

[mhalbritter]

I stumbled over that while working on #32884.