### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

There is an issue with `get-object-attributes` command which results in below error always: 
`aws --endpoint-url=http://localhost:4566 s3api get-object-attributes --bucket s3mock --key 20.txt --object-attributes "ObjectSize"`
````

> Response:  Unable to parse response (syntax error: line 1, column 0), invalid XML received. Further retries may succeed:
b'98\n5\n'
````

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

#### Using docker-compse.yaml to start localstack

docker-compse.yaml:

```
localstack:
    image: localstack/localstack:latest
    ports:
      - '4563-4599:4563-4599'
      - '8055:8080'
    environment:
      - SERVICES=s3
      - DEBUG=1
      - LS_LOG=error
      - DATA_DIR=/tmp/localstack/data
      - AWS_DEFAULT_REGION=eu-west-1
      # - EDGE_PORT=4566
    volumes:
      - "./.localstack:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"
```

#### cli commands to reproduce the issue

1. Create a Bucket: `aws --endpoint-url=http://localhost:4566 s3 mb s3://s3mock`
2. Create an Object: `aws --endpoint-url=http://localhost:4566 s3 cp data/20.txt s3://s3mock`

File 20.txt content are 2-digit numbers separated by newline.

3. get-object-attributes for object 20.txt :
```

 aws --endpoint-url=http://localhost:4566 s3api get-object-attributes --bucket s3mock --key 20.txt --object-attributes "ObjectSize"

```
Results in error:

> Unable to parse response (syntax error: line 1, column 0), invalid XML received. Further retries may succeed:
b'98\n5\n'



### Environment

```markdown
- OS:Mac 12.x
- LocalStack:latest
- Node 14
```


### Anything else?

_No response_
super(RestXMLRequesr, self).__init__(service_model)
        self.ignore_get_body_errors = True
        self._namespace_re = re.compile("{.*}")
    def _initial_body_parse(self, request: HttpRe
        body = request.data
        if not body:
            n ETree.Element("")
        n self._parse_xml_string_to_dom(body)
    def _parse_structure(
        self,
        request: HttpRequest,
        shape: StructureShape,
        node: ETree.Element,
        
    ) -> dict:
        parsed = {}
        xml_dict = self._build_name_to_xml_node(node)
        for member_name, member_shape in shape.members.items():
            xml_name = self._member_key_name(member_shape, member_name)
            member_node = xml_dict.get(xml_name)
            # If a shape defines a location trait, the node might be None (since these are extracted from the request's
            # metadata like headers or the URI)
            if (
                member_node is not None
                or "location" in member_shape.ization
                or member_shape.ization.get("eventheader")