On this page I can find the following quote:
"If your team requires stricter control, consider using branch permissions to restrict who can merge a pull request to particular users or groups"
However on the page about branch permissions there is only a possibility to
- Prevent all changes (except by user/group)
- Prevent changes without a pull request (except by user/group)
How am I supposed to restrict merging a pull requests (to master), except by a particular user or group?