Disable approval of PRs for anyone who has committed to the branch

[mwarkentin]

Currently, the person who opened the PR cannot self-approve it. However someone else can push code to the same branch, approve, and merge (bypassing branch protection meant to require review by another person before merging).

We'd love a way to prevent this through Github. We found a probot app which does basically what we want, but it would be nice to not have to host this infrastructure ourselves: https://github.com/Raul6469/self-approve

[mwarkentin]

I've opened a discussion on the official feedback forum: community/community#5337