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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description

In the `ReceiveMessageResult` of the SQS service, I saw this XML from localstack:

```
...
<MessageAttribute>
     <Name>encoding</Name>
    <Value>
        <DataType>String</DataType>
        <StringValue><![CDATA[gzip]]></StringValue>
    </Value>
</MessageAttribute>
...
```

The `<![CDATA[gzip]]>` is slightly different from AWS, which doesn't wrap the value in a `<!CDATA[[]]>` section. This shouldn't be a problem for XML parsers that accept both plain characters and CDATA sections for this element, but the XML parser I was using did not, which causes an error when running the code against localstack but not when running the code against AWS. There is obviously a bug in the XML parser as well, but I thought that I should at least post this here since it is different than what AWS SQS does.

## Expected behavior

MessageAttribute::Value elements should not be wrapped in `CDATA` sections.

## Actual behavior

MessageAttribute::Value elements all seem to be wrapped in `CDATA` sections.

# Steps to reproduce

Send a message to the SQS service which contains some custom message attributes, then make a ReceiveMessageRequest.

## Command used to start LocalStack

`docker run --env "SERVICES=sqs" localstack/localstack`

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

...

if sqs_listener.BACKEND_IMPL == 'moto':
        return start_sqs_moto(*args, **kwargs)
    return start_sqs_elasticmq(*args, **kwargs)
def patch_moto():
    
    def add_message(self, *args, **kwargs):
        mappings = self.lambda_event_source_mappings
        try:
            
            self.lambda_event_source_mappings = {}
            return add_message_orig(self, *args, **kwargs)
        finally:
            self.lambda_event_source_mappings = mappings
    add_message_orig = Queue.add_message
    Queue.add_message = add_message
    
    sqs_responses.RECEIVE_MESSAGE_RESPONSE = sqs_responses.RECEIVE_MESSAGE_RESPONSE.replace(
        '<StringValue>{{ value.string_value }}</StringValue>',
        '<StringValue><![CDATA[{{ value.string_value }}]]></StringValue>')
def start_sqs_moto(port=None, asynchronous=False, update_listener=None):
    global PORT_SQS_BACKEND
    port = port or config.PORT_SQS
    PORT_SQS_BACKEND = get_free_tcp_port()
    patch_moto()
    return start_moto_server('sqs', port, backend_port=PORT_SQS_BACKEND, name='SQS',
        asynchronous=asynchronous, update_listener=update_listener)
def start_sqs_elasticmq(port=None, asynchronous=False, update_listener=None):
    global PORT_SQS_BACKEND