204 status in generic webhook is treated as error

[makkes]

When a webhook configured through the generic or generic-hmac Provider returns an HTTP status of 204 an error is logged:

{"level":"error","ts":"2022-11-16T14:28:39.167Z","logger":"event-server","msg":"failed to send notification","reconciler kind":"HelmRelease","name":"metallb","namespace":"metallb","error":"postMessage failed: request failed with status code 204, "}

I think we should treat any 2xx status as success.