Auto-configuration samples in spring-boot-docs should be final as well

[izeye]

The checkArchitectureMain task from the spring-boot-docs fails as follows:

% ./gradlew clean :documentation:spring-boot-docs:checkArchitectureMain
...
> Task :documentation:spring-boot-docs:checkArchitectureMain FAILED
...

And failure-report.txt contains the following:

Architecture Violation [Priority: MEDIUM] - Rule 'classes that are annotated with @AutoConfiguration should be public and should have modifier FINAL' was violated (3 times):
Class <org.springframework.boot.docs.features.developingautoconfiguration.conditionannotations.beanconditions.MyAutoConfiguration> does not have modifier FINAL in (MyAutoConfiguration.java:0)
Class <org.springframework.boot.docs.features.developingautoconfiguration.conditionannotations.classconditions.MyAutoConfiguration> does not have modifier FINAL in (MyAutoConfiguration.java:0)
Class <org.springframework.boot.docs.features.developingautoconfiguration.testing.MyServiceAutoConfiguration> does not have modifier FINAL in (MyServiceAutoConfiguration.java:0)
Architecture Violation [Priority: MEDIUM] - Rule 'members that are declared in classes that are annotated with @AutoConfiguration and aren't default constructors and aren't constants and don't override public methods should not be public' was violated (2 times):
Method <org.springframework.boot.docs.features.developingautoconfiguration.conditionannotations.beanconditions.MyAutoConfiguration.someService()> has modifier PUBLIC in (MyAutoConfiguration.java:29)
Method <org.springframework.boot.docs.features.developingautoconfiguration.testing.MyServiceAutoConfiguration.userService(org.springframework.boot.docs.features.developingautoconfiguration.testing.MyServiceAutoConfiguration$UserProperties)> has modifier PUBLIC in (MyServiceAutoConfiguration.java:35)

[snicoll]

See also #32883

@izeye I don't understand this. Perhaps a cache issue but I cleaned and even ran --rerun-taks but I couldn't manage to reproduce the error above. That said, the change looks good so I am going to merge it.