Message Identification when oneOf is expected

I have an asyncapi, similar to the one below. Is there a standard way to identify the message that we receive in the channel?

For instance, In the below example, how to identify the message sent on test2 channel? How do we know if it's objectWithKey or objectWithKey2?

```yaml
asyncapi: 3.0.0
info:
title: OneOf example
version: 1.0.0
channels:
test:
address: test
messages:
testMessages:
$ref: '#/components/messages/testMessages'
test2:
address: test2
messages:
objectWithKey:
payload:
$ref: '#/components/schemas/objectWithKey'
objectWithKey2:
payload:
$ref: '#/components/schemas/objectWithKey2'
operations:
onTestMsg:
action: receive
channel:
$ref: '#/channels/test'
messages:
- $ref: '#/channels/test/messages/testMessages'
sendTest:
action: send
channel:
$ref: '#/channels/test2'
messages:
- $ref: '#/channels/test2/messages/objectWithKey'
- $ref: '#/channels/test2/messages/objectWithKey2'
components:
messages:
testMessages:
payload:
oneOf:
- $ref: '#/components/schemas/objectWithKey'
- $ref: '#/components/schemas/objectWithKey2'
testMessage1:
payload:
$ref: '#/components/schemas/objectWithKey'
testMessage2:
payload:
$ref: '#/components/schemas/objectWithKey2'
schemas:
objectWithKey:
type: object
properties:
key:
type: string
objectWithKey2:
type: object
properties:
key2:
type: string
```

Start with the AsyncAPI 3.0 example, especially channels.test2, operations.sendTest, and the objectWithKey/objectWithKey2 schemas. Determine whether the specification defines a standard discriminator or message-identification mechanism for oneOf payloads; done means the expected behavior and any required specification change are documented clearly.

Written by the indexing model from the issue text.