This enables all slash commands to also work on PRs created from forks. This will not run CI on PRs coming from a fork. There are unfortunately some limitations around injecting secrets in pull_request actions, which I described in detail in this comment.
I've done most of the testing for this in https://github.com/timroes/github-actions-test to test out that the context are set the way I'd expect them.
There's one risk: if any of the actual build scripts called by one of the slash commands would use this repository hard-coded they might fail. I've tried to search through the whole code base and don't believe this is the case.
