### 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_
self,
        s3_bucket,
        use_virtual_address,
        snapshot,
        aws_client,
        aws_client_factory,
    ):
        snapshot.add_transformers_list(
            [
                snapshot.transform.key_value("x-amz-request-id"),
                snapshot.transform.key_value("x-amz-id-2"),
                snapshot.transform.key_value("last-modified", reference_replacement=False),
                snapshot.transform.key_value("date", reference_replacement=False),
                snapshot.transform.key_value("server"),
            ]
        )
        _key = "temp.txt"
        aws_client.s3.put_(Key=_key, Bucket=s3_bucket, Body="123")
        s3_config = {"addressing_s": "virtual"} if use_virtual_address else {}
        client = aws_client_factory(
            config=Config(s3=s3_config),
            endpoint_url=_endpoint_url(),
        ).s3
        url = _generate_presigned_url(client, {"Bucket": s3_bucket, "Key": _key}, expires=10)
        response = .get(url)
        assert response.ok
        lowercase_headers = {k.lower(): v for k, v in response.headers.items()}
        snapshot.match("get-obj-content-len-headers", lowercase_headers)
    @markers.aws.validated
    def test_empty_bucket_fixture(self, s3_bucket, s3_empty_bucket, snapshot, aws_client):