Fixes a bug that was originally found by Claude and reported to the NixOS
security team by Anthropic as a security issue.
Previously, the file list was never output for merge commits.
This could have allowed someone who buried an edit to a file that shouldn't be
edited manually in a merge commit to not trigger the check.
It isn't a security issue, though, because the manual-file-edits check is not
a security boundary (just a friendly reminder to committers).
Anthropic report ID: ANT-2026-223Q3FSE
