### 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_
"""
Request parsers for the different AWS service protocols.
The module contains classes that take an HTTP request to a service, and
given an operation model, parse the HTTP request according to the
specified input shape.
It can be seen as the counterpart to the ``ize`` module in
``botocore`` (which izes the request before sending it to this
parser). It has a lot of similarities with the ``parse`` module in
``botocore``, but serves a different purpose (parsing requests
instead of responses).
The different protocols have many similarities. The class hierarchy is
designed such that the parsers share as much logic as possible.
The class hierarchy looks as follows:
::
                          ┌─────────────┐
                          │Requesr│
                          └─────────────┘
                             ▲   ▲   ▲
           ┌─────────────────┘   │   └────────────────────┐
  ┌────────┴─────────┐ ┌─────────┴───────────┐ ┌──────────┴──────────┐
  │QueryRequesr│ │BaseRestRequesr│ │BaseJSONRequesr│
  └──────────────────┘ └─────────────────────┘ └─────────────────────┘