Git’s scp-like SSH form: user@host:path whatever the path (git@host:/srv/repo.git included),
or host:path without a user unless it is host:<port>/…. A scheme:// URL or a local path is
not one.
A bare host/path URL (github.com/org/repo) spelled with https://; any other URL is
returned as written. Reading an entry applies it, so a consumer’s mars.toml and a dependency’s
manifest fetch the same repository from the same text.