### 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_
"""
    The request parser is responsible for parsing an incoming HTTP request.
    It determines which operation the request was aiming for and parses the incoming request such that the resulting
    dictionary can be used to invoke the service's function implementation.
    It is the base class for all parsers and therefore contains the basic logic which is used among all of them.
    """
    service: ServiceModel
    DEFAULT_ENCODING = "utf-8"
    # The default timestamp format is ISO8601, but this can be overwritten by subclasses.
    TIMESTAMP_FORMAT = "iso8601"
    # The default timestamp format for header fields
    HEADER_TIMESTAMP_FORMAT = "rfc822"
    def __init__(self, service: ServiceModel) -> None:
        super().__init__()
        self.service = service
    @_handle_exceptions
    def parse(self, request: HttpRequestuple[OperationModel, Any]:
        """
        Determines which operation the request was aiming for and parses the incoming request such that the resulting
        dictionary can be used to invoke the service's function implementation.
        :param request: to parse
        :n: a tuple with the operation model (defining the action / operation which the request aims for),
                 and the parsed service parameters
        :raises: RequesrError (either a ProtocolParserError or an UnknownParserError)
        """
        raise NotImplementedError
    def _parse_shape(