Do not run danger on forked projects

What does this MR do?

To avoid problems like https://gitlab.com/gitlab-renovate-forks/gitlab-pages/-/jobs/4278812426, when the renovate-bot tries to update a dependency, we'll not run danger on forks.

Related to: !871 (comment 1389551107)

TODO

• Feature flag
  • Added feature flag:
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines