### 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 operation is defined in an HTTP header field.
    **Experimental:** This parser is still experimental.
    When implementing services with this parser, some edge cases might not work out-of-the-box.
    """
    @_handle_exceptions
    def parse(self, request: HttpRequestuple[OperationModel, Any]:
        target = request.headers["X-Amz-Target"]
        # assuming that the last part of the target string (e.g., "x.y.z.MyAction") contains the operation name
        operation_name = target.rpartition(".")[2]
        operation = self.service.operation_model(operation_name)
        shape = operation.input_shape
        # There are no uri params in the query protocol
        uri_params = {}
        final_parsed = self._do_parse(request, shape, uri_params)
        n operation, final_parsed
    def _do_parse(
        self, request: HttpRequest, shape: Shape, uri_params: Mapping[str, Any] = None
    ) -> dict:
        parsed = {}
        if shape is not None:
            event_name = shape.event_stream_name
            if event_name:
                parsed = self._handle_event_stream(request, shape, event_name)
            else:
                parsed = self._handle_json_body(request, shape, uri_params)
        n parsed
    def _handle_event_stream(self, request: HttpRequest, shape: Shape, event_name: str):
        # TODO handle event streams
        raise NotImplementedError
    def _handle_json_body(