It can be confusing that some commits (typically the working copy)
don't have a description. Let's show a placeholder text in such cases.
I chose the format to match the "(no email configured)" message we
already have.
These tests are very similar to the `jj restore -i` tests because `jj
edit -r $REV` is a specialized version of `jj restore -i --from $REV-
--to $REV` on non-merge commits.