opam: Incorrect handling of packages with multiple authors

eg. https://webapp.staging.swh.network/browse/release/9798cb5ce14f78f46e35be5049d2395942f0bb33/?origin_url=opam%2Bhttps://opam.ocaml.org/packages/binsec/&release=0.4.0&snapshot=ae366bb6aac41ad022b73a8ff8534a8815aeb73c

from https://opam.ocaml.org/packages/binsec/

https://webapp.staging.swh.network/api/1/release/9798cb5ce14f78f46e35be5049d2395942f0bb33/ shows:

{
    "author": {
        "email": null,
        "fullname": "[\"Adel Djoudi\" \"Benjamin Farinier\" \"Fr\u00e9d\u00e9ric Recoules\" \"Josselin Feist\" \"Lesly-Ann Daniel\" \"Manh-Dung Nguyen\" \"Mathilde Ollivier\" \"Matthieu Lemerre\" \"Olivier Nicole\" \"Richard Bonichon\" \"Robin David\" \"Ta Thanh Dinh\" \"Ya\u00eblle Vin\u00e7ont\" \"Guillaume Girol\"]",
        "name": "[\"Adel Djoudi\" \"Benjamin Farinier\" \"Fr\u00e9d\u00e9ric Recoules\" \"Josselin Feist\" \"Lesly-Ann Daniel\" \"Manh-Dung Nguyen\" \"Mathilde Ollivier\" \"Matthieu Lemerre\" \"Olivier Nicole\" \"Richard Bonichon\" \"Robin David\" \"Ta Thanh Dinh\" \"Ya\u00eblle Vin\u00e7ont\" \"Guillaume Girol\"]"
    },
    "date": null,
    "id": "9798cb5ce14f78f46e35be5049d2395942f0bb33",
    "message": "0.4.0",
    "name": "0.4.0",
    "synthetic": true,
    "target": "c593872c2fb03ee0fd8beed282b214575687690b",
    "target_type": "directory",
    "target_url": "https://webapp.staging.swh.network/api/1/directory/c593872c2fb03ee0fd8beed282b214575687690b/"
}

---

Migrated from T4602 (view on Phabricator)