In version 78.v2dcf62ba199b GitHub Pull Request Comment Build Plugin
introduced permissions check for users triggering jobs with comments.
This added a new checkbox/XML element that allows untrusted users to
trigger builds.
(see https://github.com/jenkinsci/github-pr-comment-build-plugin/pull/46)
This commit adds support for this option by allowing dictionary syntax for GH PR Comment Build plugin:
```
- trigger-build-on-pr-review:
allow-untrusted-users: true
```
while preserving support for currently existing syntax:
```
- trigger-build-on-pr-review: true
```
Change-Id: I554129c779161b47cba4566f7821ef7590a242e0
5cea04aa2a