Unable to publish due to key verification failure

[kit-ty-kate]

Moved from ocaml/opam#5620

The following will be published:
  - camlpdf version 2.6 with opam file at /Users/john/repos/camlpdf/camlpdf.opam
    archive at https://github.com/johnwhitington/camlpdf/archive/refs/tags/v2.6.tar.gz


You will be shown the patch before submitting.
Please confirm the above data. Continue ?  [Y/n] Y
Please generate a Github token at https://github.com/settings/tokens/new to allow access.
The "public_repo" scope is required ("repo" if submitting to a private opam repository).

Please enter your GitHub personal access token: 
The token will be stored in ~/.opam/plugins/opam-publish/ocaml%opam-repository.token.
Cloning the package repository, this may take a while...
+ /usr/bin/git "clone" "[email protected]:ocaml/opam-repository.git" "/Users/john/.opam/plugins/opam-publish/repos/ocaml%opam-repository"
The authenticity of host 'github.com (140.82.121.4)' can't be established.
ED25519 key fingerprint is SHA256:+<elided>
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? - Cloning into '/Users/john/.opam/plugins/opam-publish/repos/ocaml%opam-repository'...

- Host key verification failed.
- fatal: Could not read from remote repository.
- 
- Please make sure you have the correct access rights
- and the repository exists.
[ERROR] Uncaught exception: "/usr/bin/git clone [email protected]:ocaml/opam-repository.git
        /Users/john/.opam/plugins/opam-publish/repos/ocaml%opam-repository" exited with code 128

cc @johnwhitington

[kit-ty-kate]

See #156 (comment) for what the original issue was and potential solutions