Fix type pollution RabbitListenerAnnotationBeanPostProcessor

[dreis2211]

Hi 👋

I've been recently playing with the https://github.com/RedHatPerf/type-pollution-agent from @franz1981 and found that RabbitListenerAnnotationBeanPostProcessor - more specifically findListenerAnnotations - seems to be causing the TOP 3 for us during startup.

3:      java.util.ArrayList
Count:  16432
Types:
        java.util.List
        java.util.Collection
        java.lang.Iterable
Traces:
        org.springframework.amqp.rabbit.annotation.RabbitListenerAnnotationBeanPostProcessor.findListenerAnnotations(Rabbi
tListenerAnnotationBeanPostProcessor.java:345)
                class: java.util.Collection
                count: 8123
        org.springframework.core.annotation.TypeMappedAnnotations.getAggregates(TypeMappedAnnotations.java:226)
                class: java.util.List
                count: 7905
...

The method returns Collection (and has corresponding type cast internally), while it returns a List really. Everyone else in the traces seems to use largely List as well (see the next trace e.g.). Even if this is a false-positive in terms of actual type pollution it seems like a simple enough fix to be on the safe side. I'll provide a PR shortly where further discussion can happen, but I needed this issue to stick to the commit convention ;-)

Cheers,
Christoph