### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When you publish a message to SNS without a *body* (e.g. only attributes) it succeeds.

### Expected Behavior

Trying to publish a message without a *body* should fail (at least it does when trying to do this in AWS)

### How are you starting LocalStack?

Custom (please describe below)

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

using Java testcontainers...

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

```bash
#!/bin/sh
 
queue_arn=$(awslocal sqs create-queue --queue-name $QUEUE_NAME --output text)
echo "Queue ARN: $queue_arn"

topic_arn=$(awslocal sns create-topic --name $TOPIC_NAME --output text)
echo "Topic ARN: $topic_arn"

subscription_arn=$(awslocal sns subscribe \
    --attributes RawMessageDelivery=true \
    --topic-arn "$topic_arn" \
    --protocol sqs \
    --notification-endpoint "$queue_arn" \
    --output text)
echo "Subscription ARN: $subscription_arn" 
```


### Environment

```markdown
- OS: OSX 11.5.2
- LocalStack: 0.13.0
- Docker Desktop: v20.10.8
```


### Anything else?

_No response_
self.assertGreater(len(sns_backend.platform_endpoint_messages[platform_arn]), 0)
        retry(check_message, retries=PUBLICATION_RETRIES, sleep=PUBLICATION_TIMEOUT)
        # c
        sns.unsubscribe(SubscriptionArn=subscription["SubscriptionArn"])
        sns.delete_endpoint(EndpointArn=platform_arn)
        sns.delete_platform_application(PlatformApplicationArn=app_arn)
    def _publish_sns_message_with_attrs(self, endpoint_arn, protocol):
        # c
        filter_policy = {"attr1": [{"numeric": [">", 0, "<=", 100]}]}
        subscription = self.sns_client.subscribe(
            TopicArn=self.topic_arn,
            Protocol=protocol,
            Endpoint=endpoint_arn,
            Attributes={"FilterPolicy": json.dumps(filter_policy)},
        )
        # p
        message = "This is a test message"
        self.sns_client.publish(
            TopicArn=self.topic_arn,
            Message=message,
            MessageAttributes={"attr1": {"DataType": "Number", "StringValue": "99.12"}},
        )
        time.sleep(PUBLICATION_TIMEOUT)
        return subscription
    def test_unknown_topic_publish(self):