fix(ns-asyncapi-2-0): fix typo in specification object

Refs #387

Author: char0n

apidom/packages/apidom-ns-asyncapi-2-0/src/refractor/specification.ts

@@ -435,7 +435,7 @@ const specification = {
           },
         },
         Tags: {
-          $visitors: TagsVisitor,
+          $visitor: TagsVisitor,
         },
         Tag: {
           $visitor: TagVisitor,

apidom/packages/apidom-ns-asyncapi-2-0/src/refractor/visitors/async-api-2-0/message/index.ts

@@ -37,7 +37,7 @@ const MessageVisitor = stampit(FixedFieldsVisitor, FallbackVisitor, {
         'application/vnd.aai.asyncapi;version=2.0.0',
         objectElement.get('schemaFormat')?.toValue(),
       );
-      const payload = objectElement.get('payload');
+      const payload = this.element.get('payload');
       this.refractPayload(schemaFormat, payload);
 
       return result;