fix: oneOf should not be allowed in message components (#345)

Author: jonaslagoni

definitions/3.0.0/components.json

@@ -21,7 +21,19 @@
       "$ref": "http://asyncapi.com/definitions/3.0.0/serverVariables.json"
     },
     "messages": {
-      "$ref": "http://asyncapi.com/definitions/3.0.0/messages.json"
+      "type": "object",
+      "patternProperties": {
+        "^[\\w\\d\\.\\-_]+$": {
+          "oneOf": [
+            {
+              "$ref": "http://asyncapi.com/definitions/3.0.0/Reference.json"
+            },
+            {
+              "$ref": "http://asyncapi.com/definitions/3.0.0/messageObject.json"
+            }
+          ]
+        }
+      }
     },
     "securitySchemes": {
       "type": "object",