attrpathsSuperset got renamed to preEval in nixpkgs[1] breaking Hydra's
evaluation. Updating nixpkgs to make sure this is consistent now, no
matter if flake-inputs or release.nix is being used.
[1] See commit 19a31658dc39324c9acf8d81198cd7137bdc1e92.
Change-Id: I69ab3f894534b1d89b626ddd4feda8ea502b69b3