dev/pr-auditor: run on pull_request_target
Created by: bobheadxi
https://github.com/sourcegraph/sourcegraph/pull/35675, which fixes pr-auditor's ability to set commit statuses on PRs coming from forks, was mistakenly reverted in https://github.com/sourcegraph/sourcegraph/pull/36798
I'll update https://k8s.sgdev.org/users/robert/batch-changes/pr-auditor-patch-06-16 with this change
Test plan
was previously tested