### 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_
response = aws_client.lambda_.invoke(FunctionName=function_name)
        payload = json.load(response["Payload"])
        presigned_url = payload["body"].strip('"')
        assert "=AES256" in presigned_url
        # AWS 
        response = .put(presigned_url, verify=False, data=b"123456")
        assert response.status_code == 403
        # asse
        # beca
        response = .put(
            presigned_url,
            data=b"123456",
            verify=False,
            headers={"Content-MD5": "4QrcOUm6Wau+VuBX8g+IPg=="},
        )
        assert response.status_code == 200
        # asse
        # it w
        response = .put(
            presigned_url,
            data=b"123456",
            verify=False,
            headers={
                "Content-MD5": "4QrcOUm6Wau+VuBX8g+IPg==",
                "x-amz-server-side-encryption": "AES256",
            },
        )
        assert response.status_code == 200
    @markers.aws.validated
    def test_pre_signed_url_forward_slash_bucket(