Fix row format diffing

[morgo]

A Pull Request should be associated with an Issue.

We wish to have discussions in Issues. A single issue may be targeted by multiple PRs.
If you're offering a new feature or fixing anything, we'd like to know beforehand in Issues,
and potentially we'll be able to point development in a particular direction.
Further notes in https://github.com/block/spirit/blob/main/.github/CONTRIBUTING.md

This is a followup to #598