Note Hook is not supported for this project

## Issue

### Context
- **Gitlab plugin version**: 1.5.11
- **Gitlab version**: 11.3.5-ee
- **Jenkins version**: 2.173
- **Job type**: Multibranch Pipeline

### Logs & Traces
https://gist.github.com/wdlaszlo/a4d228aff53ca35b397cdeb60c5223f1
https://gist.github.com/wdlaszlo/aec5e1b29a8c2e7ae51359274937dd1c

### Problem description
I want to trigger the Multibranch Pipeline job in Jenkins when I add a comment on GitLab MR, but it fails.

Expectations:
To trigger my job, exactly how it works when I make a change into the repo.

Current results:
I receive an 409 error, see second gist.