What is the current behaviour and why should it be changed?
Git is confusing - especially for new contributors.
Contributors might be confused how to update their PRs and merge instead of rebase. We should explain the process of interactive rebase with conflicts.

Describe possible approaches

Link https://teamairship.com/update-outdated-branch-without-creating-merge-commit/ or similar somewhere or give explanations in CONTRIBUTING.md

Has this feature been discussed and generally agreed?

No