Consider using nix-quick-install in GitHub workflows.

[Zimmi48]

I haven't tested it yet, but https://github.com/marketplace/actions/nix-quick-install is advertised as being 4 times faster than the install-nix-action that we are currently using. For the workflows in this repository, given the very large number of jobs that we trigger (many of them only to quickly succeed after checking that an output is already in cache), it seems like the gain of time would be worth, if it works.