### 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_
if method == "OPTIONS":
            return 200
        
        try:
            aws_stack.check_valid_region(headers)
            aws_stack.set_default_region_in_headers(headers)
        except Exception as e:
            return make_error(message=str(e), code=400)
        if method == "POST":
            
            req_data = urlparse.parse_qs(to_str(data), keep_blank_values=True)
            
            if not req_data:
                parsed_path = urlparse.urlparse(path)
                req_data = urlparse.parse_qs(parsed_path.query, keep_blank_values=True)
            req_action = req_data["Action"][0]
            topic_arn = (
                req_data.get("TargetArn") or req_data.get("TopicArn") or req_data.get("ResourceArn")
            )
            if topic_arn:
                topic_arn = topic_arn[0]
                topic_arn = aws_stack.fix_account_id_in_arns(topic_arn)
            if req_action == "SetSubscriptionAttributes":
                sub = get_subscription_by_arn(req_data["SubscriptionArn"][0])
                if not sub:
                    return make_error(message="Unable to find subscription for given ARN", code=400)
                attr_name = req_data["AttributeName"][0]
                attr_value = req_data["AttributeValue"][0]
                sub[attr_name] = attr_value
                return make_response(req_action)