### 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_
)
        snapshot.match(f"{snapshot_prefix}-compete-multipart", response)
        return response
    return perform_multipart_upload
@pytest.fixture
def create_tmp_folder_lambda():
    cleanup_folders = []
    def prepare_folder(path_to_lambda, run_command=None):
        tmp_dir = tempfile.mkdtemp()
        shutil.copy(path_to_lambda, tmp_dir)
        if run_command:
            run(f"cd {tmp_dir}; {run_command}")
        cleanup_folders.append(tmp_dir)
        return tmp_dir
    yield prepare_folder
    for folder in cleanup_folders:
        try:
            shutil.rmtree(folder)
        except Exception:
            LOG.warning(f"could not delete folder {folder}")
@pytest.fixture
def allow_bucket_acl(s3_bucket, aws_client):
    """
    # Since April 2023, AWS will by default block setting ACL to your bucket and . You need to manually disable
    # the BucketOwnershipControls and PublicAccessBlock to make your s public.
    # See https://aws.amazon.com/about-aws/whats-new/2022/12/amazon-s3-automatically-enable-block-public-access-disable-access-control-lists-buckets-april-2023/
    """
    aws_client.s3.delete_bucket_ownership_controls(Bucket=s3_bucket)
    aws_client.s3.delete_public_access_block(Bucket=s3_bucket)
def _filter_header(param: dict) -> dict: