Not able to exclude master from being triggered

## Issue

I would like to have two different jobs for building the feature-branch/MR and master. For this reason I created a second job pulling master every hour (if there are changes).
Now I would like to prevent the plugin to a start build when pushing on master. It should only build on every other branch.
When adding master to excluded branches by name it has no effect (just a warning 'Following patterns don't match any branch in source repository: master')

### Context
- **Gitlab plugin version**: 1.5.11
- **Gitlab version**: 11.8.2
- **Jenkins version**: 2.164.1
- **Job type**: maven

### Logs & Traces

### Problem description

1.) When I push a change an master I expect that the build is not triggered but the build is triggered.
2.) When I create a MR or do a push the MR I expect that the build is triggered (is working like expected).