Don't check trusted members on non-fork merge requests to reduce GitLab API calls

[The-Jonsey]

Preventing calling gitlab api to get all members on project for non-fork merge requests in getTrustedRevision, hopefully helps with #515

Testing done

Tested on a jenkins instance, fork builds were not tested as none of the projects this jenkins can touch can be forked, but origin merge requests worked as intended.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[q2-kkendall]

This is super, hopefully it can get some eyes on it soon.