Fix to improve security around creation of pull requests in public repos

We've shipped a small fix to improve security around creation of pull requests in public repos.

Prior to this fix and under very specific conditions, a user could create a pull request in a public repo even though they did not have push access to either the base or head branch and were not a member of the repo's organization. Often these pull requests were created by mistake and quickly closed, but could still trigger unexpected GitHub Actions or other CI jobs.

This fix has no impact on the common open source workflow where a user forks a public repo, makes a change in their fork, and then proposes their change using a pull request. This fix also has no impact on pull requests already created.

We want to hear from you! Let us know if you have questions or feedback.