Once a pull request is approved, if there are further commits:
The Pull request should go to un-approved state automatically.
Can this be done?
The ability to Dismiss stale pull request approvals when new commits are pushed is a setting under Require pull request reviews before merging in the branch protection settings. This is disabled by default.
This isn't currently offered.
You can create an application that listens for push webhook events, queries the API for all Reviews for a Pull Request, and dismisses any that are APPROVED.
Here is a Ruby script you could host on heroku.
来源：https://stackoverflow.com/questions/41824374/how-to-un-approve-github-review-after-new-commits-automatically