### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
)
        anon = anonymous_client("s3")
        anon.put_(
            Bucket=s3_bucket,
            Key=_key_2,
            Body="This body document #2",
            ACL="public-read-write",
        )
        url = f"{_bucket_url(s3_bucket, localstack_host=get_localstack_host().host)}?delete"
        data = f"""
        <Delete xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
          <>
            <Key>{_key_1}</Key>
          </>
          <>
            <Key>{_key_2}</Key>
          </>
        </Delete>
        """
        md = hashlib.md5(data.encode("utf-8")).digest()
        contents_md5 = base64.b64encode(md).decode("utf-8")
        header = {"content-md5": contents_md5, "x-amz-request-payer": "requester"}
        r = .post(url=url, data=data, headers=header)
        assert 200 == r.status_code
        response = xmltodict.parse(r.content)
        response["DeleteResult"].pop("@xmlns", None)
        assert response["DeleteResult"]["Error"]["Key"] == _key_1
        assert response["DeleteResult"]["Error"]["Code"] == "AccessDenied"
        assert response["DeleteResult"]["Deleted"]["Key"] == _key_2
        snapshot.match("multi-delete-with-", response)