### 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_
@markers.aws.only_localstack
    def test_terraform_request_sequence(self, aws_client):
        reqs = load_file(
            os.path.join(
                os.path.dirname(__file__),
                "../../files/s3..txt",
            )
        )
        reqs = reqs.split("---")
        for req in reqs:
            header, _, body = req.strip().partition("\n\n")
            req, _, headers = header.strip().partition("\n")
            headers = {h.split(":")[0]: h.partition(":")[2].strip() for h in headers.split("\n")}
            method, path, _ = req.split(" ")
            url = f"{config.internal_service_url()}{path}"
            result = .request(method=method, url=url, data=body, headers=headers)
            assert result.status_code < 400
class TestS3PresignedUrl:
    """
    These tests pertain to S3's  feature.
    """
    # # Note: This test may have side effects (via `s3_client.meta.events.register(..)`) and
    # # may not be suitable for parallel execution
    @markers.aws.validated
    def test_presign_with_additional_query_params(