### 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_
▲                    ▲            ▲   ▲           ▲
  ┌───────┴────────┐ ┌─────────┴──────────┐ │   │           │
  │EC2Requesr│ │RestXMLRequesr│ │   │           │
  └────────────────┘ └────────────────────┘ │   │           │
                           ┌────────────────┴───┴┐ ┌────────┴────────┐
                           │RestJSONRequesr│ │JSONRequesr│
                           └─────────────────────┘ └─────────────────┘
::
The ``Requesr`` contains the logic that is used among all the
different protocols (``query``, ``json``, ``rest-json``, ``rest-xml``,
and ``ec2``).
The relation between the different protocols is described in the
``izer``.
The classes are structured as follows:
* The ``Requesr`` contains all the basic logic for the parsing
  which is shared among all different protocols.
* The ``BaseRestRequesr`` contains the logic for the REST
  protocol specifics (i.e. specific HTTP metadata parsing).
* The ``BaseJSONRequesr`` contains the logic for the JSON body
  parsing.
* The ``RestJSONRequesr`` inherits the ReST specific logic from
  the ``BaseRestRequesr`` and the JSON body parsing from the
  ``BaseJSONRequesr``.
* The ``QueryRequesr``, ``RestXMLRequesr``, and the
  ``JSONRequesr`` have a conventional inheritance structure.
The services and their protocols are defined by using AWS's Smithy
(a language to define services in a - somewhat - protocol-agnostic
way). The "peculiarities" in this parser code usually correspond
to certain so-called "traits" in Smithy.
The result of the parser methods are the operation model of the