### 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_
"""
        This method executes the initial parsing of the body (XML, JSON, or CBOR).
        The parsed body will afterwards still be walked through and the nodes will be converted to the appropriate
        types, but this method does the first round of parsing.
        :param request: of which the body should be parsed
        :n: depending on the actual implementation
        """
        raise NotImplementedError("_initial_body_parse")
    e_event_stream(self, request: HttpRequest, shape: Shape) -> Any:
        # TODO handle event streams
        raise NotImplementedError("_create_event_stream")
class RestXMLRequesr(BaseRestRequesr):
    """
    The ``RestXMLRequesr`` is responsible for parsing incoming requests for services which use the ``rest-xml``
    protocol. The requests for these services encode the majority of their parameters as XML in the request body.
    **Experimental:** This parser is still experimental.
    When implementing services with this parser, some edge cases might not work out-of-the-box.
    """
    def __init__(self, service_model: ServiceModel):