Authenticate a channel

[Jeremy Korwin-Zmijowski]

Dear Guixters,

I have made an authenticated channel at 
https://framagit.org/jeko/guix-jeko-channel

While on the initial commit 60d0b6b2, I was able to `guix pull` with no 
issue.

But two days ago, I pushed a new signed commit (`git log 
--show-signature` can tell).

I haven't change anything with my keys since then. So I was surprised to 
see `guix pull` returning :

   guix pull: erreur : could not authenticate commit
   ad4cea635090b30d259dcf1cb690f07c831f6a1e: key EFBB 9626 457A C7F6
   FAED  FA70 A2E0 F15D BF8E A5F0 is missing

I don't really need to authenticate my channel as I am the only one 
making changes on it.

This was an experiment to learn. I struggled a lot to set it up.

I am currently running Guix on top of Ubuntu.

I would be grateful for any help or hint.

Cheers, take care.

Jeremy