This Action fails on Pull Requests that include merge commits.
This rule is designed to prevent developers from merging the default branch into their branch as a way of making it up-to-date. This creates foxtrot commits and confusing git log graphs.
This rule is also designed to prevent using GitHub's "Update Branch" button, which merges the base branch into the source branch. Instead, use the pull-down "Rebase Branch" button which rebases the source branch onto the base branch. This is a common problem if "Always suggest updating pull request branches" is enabled, because "Update Branch" is the default choice in the pull-down and it cannot be disabled or changed.
Full Changelog: https://github.com/motlin/forbid-merge-commits-action/commits/v1.0.0