Based on the Nixpkgs used and the version of nixfmt-rfc-style in that
version, it's likely that not the correct version is used.
Update scripts should instead run within a Nixpkgs development shell
(`nix-shell`/`nix develop`/`direnv`), where the correct version of
`nixfmt` (although `treefmt` should be preferred) is always available.
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