The divergent changes are marked with ?? (I found a single ? a bit easy to
overlook), and this should be consistent.
Ideally, the conflicted branches would also be red, but this takes a bit
larger changes to `templater.rs`: another `Property` as well as changes to
https://github.com/martinvonz/jj/blob/7f9a0a28/src/template_parser.rs#L385-L395