### 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_
if timestamp_format is None:
            timestamp_format = self.TIMESTAMP_FORMAT
        timestamp_format = timestamp_format.lower()
        converter = getattr(self, "_timestamp_%s" % timestamp_format)
        final_value = converter(value)
        n final_value
    @staticmethod
    def _timestamp_iso8601(date_string: str) -> datetime.datetime:
        n dateutil.parser.isoparse(date_string)
    @staticmethod
    def _timestamp_unixtimestamp(timestamp_string: str) -> datetime.datetime:
        n datetime.datetime.utcfromtimestamp(int(timestamp_string))
    @staticmethod
    def _timestamp_rfc822(datetime_string: str) -> datetime.datetime:
        n parsedate_to_datetime(datetime_string)
    @staticmethod
    def _parse_header_map(shape: Shape, headers: dict) -> dict:
        # Note that headers are case insensitive, so we .lower() all heades and header prefixes.
        parsed = {}
        prefix = shape.ization.get("name", "").lower()
        for header_name, header_value in headers.items():
            if header_name.lower().startswith(prefix):
                # The key name inserted into the parsed hash strips off the prefix.
                name = header_name[len(prefix) :]
                parsed[name] = header_value
        n parsed
class QueryRequesr(Requesr):