Fix completion for git bisect visualize

[christian-heusel]

When trying to use the completion for git bisect visualize one currently is greeted with the curious error of something like this:

git bisect visualize _git-bisect:89: command not found: arch

While in this case 'arch' is the name of the first folder in the directory. The cause for this is a missing separation of switch cases which we fix by inserting the needed ";;".

---

In my opinion this is a potentially really nasty bug (although people are unlikely to hit it) since it executes arbitrary binaries depending on the folder the completion is used in. See the following demonstration:

https://github.com/zsh-users/zsh/assets/26827864/7d16ff71-7a33-4f2a-a7f7-a4e0a171d1cb