### 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_
role_name, role_arn = create_role_with_policy(
            effect="Allow",
            actions=actions,
            assume_policy_doc=assume_policy_doc,
            resource="*",
        )
        credentials = wait_and_assume_role(role_arn=role_arn)
        client = boto3.client(
            "s3",
            config=Config(signature_version="s3v4"),
            endpoint_url=_endpoint_url(),
            aws_access_key_id=credentials["AccessKeyId"],
            aws_secret_access_key=credentials["SecretAccessKey"],
            aws_session_token=credentials["SessionToken"],
        )
        retry(
            lambda: s3_create_bucket_with_client(s3_client=client, Bucket=bucket_name),
            sleep=3 if is_aws_cloud() else 0.5,
        )
        client.put_(Body="test-value", Bucket=bucket_name, Key=key_name)
        presigned_url = client.generate_presigned_url(
            ClientMethod="get_",
            Params={"Bucket": bucket_name, "Key": key_name},
            ExpiresIn=600,
        )
        response = .get(presigned_url)
        assert response._content == b"test-value"
    @markers.aws.validated
    @pytest.mark.parametrize("signature_version", ["s3", "s3v4"])
    def test_s3_get_response_header_overrides(