You can require people to resolve merge conflicts locally by disabling the merge conflict editor on GitHub Enterprise for pull requests where the base branch and the head branch are in different repositories.
Requiring users to resolve merge conflicts locally on their computer can prevent people from inadvertently writing to an upstream repository from a fork.
In the upper-right corner of any page, click .
In the left sidebar, click Admin center.
Under "Conflict editor for pull requests between repositories", use the drop-down menu, and click Disabled.