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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)

...

AttributeNames=['MessageRetentionPeriod', 'RedrivePolicy']
        )
        supported_attribute_get = self.client.get_queue_attributes(QueueUrl=queue_url,
                                                                   AttributeNames=['QueueArn'])
        
        self.assertTrue('MessageRetentionPeriod' in unsupported_attribute_get['Attributes'].keys())
        self.assertEqual('604800', unsupported_attribute_get['Attributes']['MessageRetentionPeriod'])
        self.assertTrue('QueueArn' in supported_attribute_get['Attributes'].keys())
        self.assertTrue('RedrivePolicy' in unsupported_attribute_get['Attributes'].keys())
        redrive_policy = json.loads(unsupported_attribute_get['Attributes']['RedrivePolicy'])
        self.assertTrue(isinstance(redrive_policy['maxReceiveCount'], int))
        
        self.client.delete_queue(QueueUrl=queue_url)
        self.client.delete_queue(QueueUrl=dead_queue_url)
    def test_set_unsupported_attributes(self):
        queue_name = 'queue-%s' % short_uid()
        queue_url = self.client.create_queue(QueueName=queue_name)['QueueUrl']
        self.client.set_queue_attributes(
            QueueUrl=queue_url,
            Attributes={
                'FifoQueue': 'true'
            }
        )
        rs = self.client.get_queue_attributes(QueueUrl=queue_url, AttributeNames=['All'])
        self.assertEqual(rs['ResponseMetadata']['HTTPStatusCode'], 200)
        self.assertIn('FifoQueue', rs['Attributes'])
        self.assertEqual(rs['Attributes']['FifoQueue'], 'true')
        
        self.client.delete_queue(QueueUrl=queue_url)
    def test_list_dead_letter_source_queues(self):