"opam repo add" fails if one of the packages in the repository has an unsupported version

[kit-ty-kate]

$ tree
.
├── packages
│   └── a
│       └── a.1
│           └── opam
└── repo

4 directories, 2 files

$ cat packages/a/a.1/opam
opam-version: "3.0"

$ cat repo
opam-version: "2.0"

$ opam repo add test .
[test] Initialised
[ERROR] Could not update repository "test": In
        $OPAMROOT/.opam/repo/test/packages/a/a.1/opam:
        unsupported or missing file format version; should be 2.0 or older
[ERROR] Initial repository fetch failed

The expected behaviour would be do silently mark the package as unavailable and only fail when the repo file’s version is unsupported.