Cannot transition status via :enqueue from :pending

## Issue

There are error messages in the Jenkins log of the Gitlab plugin. However, the plugin seems to be doing everything it needs to do. When the plugin wants to update the Gitlab pipeline it gets a reply
```
Cannot transition status via :enqueue from :pending (Reason(s): Status cannot transition via "enqueue")
```

### Context
- **Gitlab plugin version**: 1.5.9
- **Gitlab version**: 11.2.3-ee
- **Jenkins version**: 2.121.3
- **Job type**: Pipeline

### Logs & Traces

In the Jenkins log for each trigger there is a an error with these details
```
Response body: {
"message" : "Cannot transition status via :enqueue from :pending (Reason(s): Status cannot transition via \"enqueue\")"
}

Failed to update Gitlab commit status for project '118'
javax.ws.rs.BadRequestException: HTTP 400 Bad Request
at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.handleErrorStatus(ClientInvocation.java:197)
at org.jboss.resteasy.client.jaxrs.internal.proxy.extractors.DefaultEntityExtractorFactory$3.extractEntity(DefaultEntityExtractorFactory.java:50)
at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientInvoker.invoke(ClientInvoker.java:104)
at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientProxy.invoke(ClientProxy.java:64)
...
```

### Problem description

As far as I can see, everything works as expected. The Jenkins pipeline is triggered the way it should. In GitLab the pipeline is correctly marked as `passed`. It's just that the Jenkins log shows this error.