Previously, users of the components.index could not use the index in
scenario where Spring Boot needs to locate the SpringBootConfiguration
to use to bootstrap the test context, as AnnotatedClassFinder scans
the classpath for that stereotype specifically and that requires a
dedicated entry for it.
This commit makes sure that a SpringBootConfiguration-annotated type has
a dedicated entry in the components index.
Closes gh-26308
3f528bb0eb