Upgrade to nix 2.4

[zupo]

Since nix 2.4 was released, the hourly Image Update GHActions tasks have been failing.

I've temporarily fixed them by pinning nix to a 2.3.x release: #15

Remove my temporary pin and fix the 2.4 failures.

It might make sense to update cachix/install-nix-action@v12 and cachix/cachix-action@v8 in https://github.com/niteoweb/nix-docker-base/blob/master/.github/workflows/push.yml too.

[zupo]

@NorfairKing: any progress on this?

[NorfairKing]

@zupo Not yet but I'm going to try again today.

[NorfairKing]

There is something very weird going on with reproducibility. I haven't figured out what it is but this turns out to not be as simple as we'd like.

[NorfairKing]

It looks like the project from which this repository was forked doesn't have these issues, so that gives me a lead to figure out what's going on. I'll get back about this.

[NorfairKing]

@zupo can you tell me a bit more about why this is a fork in the first place?

[NorfairKing]

nix-community/docker-nixpkgs@7cbf862

It looks like the origin didn't have any issues here, so I'm guessing they've done something that prevented the current issue ahead of time.

[zupo]

@NorfairKing: IIUC, @infinisil started it as a fork, but then rewrote most of it. So I am not sure if we can take a lot of learnings from what upstream is doing.

[infinisil]

I recently discovered that it's possible to detach forks here: https://support.github.com/request/fork. I think this would be good for this repository, as this doesn't really share much with the original

[zupo]

Requested a detach.