Do not auto run CI on forked PRs (#432)
Do not auto run CI on forked PRs (#432)

I misunderstood the security boundary for the pull_request_target event.
Apparently we should not be running code from forked PRs as it can gain
access to the github token which has access to our github secrets.

https://securitylab.github.com/research/github-actions-preventing-pwn-requests
looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen