### 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_
# upda
        empty_retention = aws_client.s3.put__retention(
            Bucket=s3_bucket_lock,
            Key=_key,
            Retention={},
            BypassGovernanceRetention=True,
        )
        snapshot.match("put--empty-retention", empty_retention)
        update_retention = aws_client.s3.put__retention(
            Bucket=s3_bucket_lock,
            Key=_key,
            Retention={
                "Mode": "GOVERNANCE",
                "RetainUntilDate": datetime.datetime.utcnow() + datetime.timedelta(seconds=5),
            },
        )
        snapshot.match("update-retention-", update_retention)
        # dele
        with pytest.raises(ClientError):
            aws_client.s3.delete_(Bucket=s3_bucket_lock, Key=_key, VersionId=version_id)
        # dele
        sleep = 10 if is_aws_cloud() else 6
        time.sleep(sleep)
        aws_client.s3.delete_(
            Bucket=s3_bucket_lock,
            Key=_key,
            VersionId=version_id,
        )
    @markers.aws.validated
    def test_s3_copy__retention_lock(self, s3_create_bucket, snapshot, aws_client):