### 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_
endpoint_url=_endpoint_url(),
        )
        url = presigned_client.generate_presigned_url(
            "get_", Params={"Bucket": s3_bucket, "Key": _key}, ExpiresIn=5
        )
        parsed = urlparse(url)
        query_params = parse_qs(parsed.query)
        # sig v2
        if "Signature" in query_params:
            query_params.pop("Expires", None)
        else:  # sig v4
            query_params.pop("X-Amz-Date", None)
        new_query_params = urlencode(
            {k: v[0] for k, v in query_params.items()}, quote_via=quote, safe=" "
        )
        invalid_url = urlunsplit(
            SplitResult(  # noqa
                parsed.scheme, parsed.netloc, parsed.path, new_query_params, parsed.fragment
            )
        )
        resp = .get(invalid_url, verify=False)
        assert resp.status_code in [
            400,
            403,
        ]  # the 
        exception = xmltodict.parse(resp.content)
        exception["StatusCode"] = resp.status_code
        snapshot.match("missing-param-exception", exception)
    @markers.aws.validated
    def test_s3_get_response_content_type_same_as_upload_and_range(self, s3_bucket, aws_client):