Fixes #776

Problem

In RocketMQMessageListenerBeanPostProcessor.buildEnhancer(), the lambda accumulates
enhanced annotation attributes into newAttrs across all registered AnnotationEnhancer
beans, but then returns the original attrs instead of newAttrs.

This means every AnnotationEnhancer bean is silently a no-op — its attribute
modifications are computed but thrown away.

Fix

Return newAttrs instead of attrs.

// before
return attrs;

// after
return newAttrs;

Root Cause

buildEnhancer() (line 178–184):

this.enhancer = (attrs, element) -> {
    Map<String, Object> newAttrs = attrs;
    for (AnnotationEnhancer enh : enhancers) {
        newAttrs = enh.apply(newAttrs, element);
    }
    return attrs;   // BUG: should be newAttrs
};

Impact

Any application that relies on AnnotationEnhancer to dynamically override @RocketMQMessageListener attributes (e.g. injecting topic/group from environment properties) will find their customizations have no effect.