Upload emacs-git packages to cachix

[slotThe]

Hi,

currently, there are hydra jobs to build packages for emacs and emacs-unstable, so that they can be cached and users do not have to rebuild every elisp package themselves. Fast to build as many are, this can otherwise take 3–5 minutes for a moderate number of packages (~200–400).

However, I'd wager a not-insignificant number of users using the overlay are actually building (or, rather, downloading) a more recent build of Emacs, like emacs-git. I would therefore advocate for adding at least packages-git to the current set of packages that are shipped to cachix.

What do people think?

[Icy-Thought]

I most certainly would agree and appreciate this change! Because rebuilding emacs-git on my low-end laptop is a rather time-consuming task.