Prefer "Rebase Merging"

I think preserving the commit history of the head branches of PRs when merging can provide value: prefer ["Rebase Merging"][rebase-merge] over the current "Squash Merging" approach. @devoto13 ?

[rebase-merge]: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/about-merge-methods-on-github#rebasing-and-merging-your-commits

Start by reading the linked GitHub documentation on rebasing and merging. The issue names no repository file or test; done would require maintainer agreement on changing the preferred merge method and a clear repository-level record of that decision.

Written by the indexing model from the issue text.