I've heard the term used for servers before but not version control repositories. I just don't understand what it would mean for a git repo to be a cattle vs a pet. Like what is an example of a cattle repo vs a pet repo. The metaphore just sounds like gibberish to me idk.
Unless all it means is that that you can have more than a few like the other commenter said but I didn't think that was what the metaphore meant with respect to servers so again I have no idea lol
To me it would mean that a git repo should not have scripts, runners, etc. configured that we don't have the means to easily and readily replace. It should all be documented and understood well enough that we could kill the repo and init another at will.