flake: Bump nixpkgs to 25.11

[xokdvium]

Motivation

25.11 is out and we should follow suit.

Context

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[Radvendii]

Nixpkgs changed so that separateDebugInfo = true; and setting {dis,}allowed{References,Requisites} now requires __structuredAttrs = true;

When I tried to fix that by setting __structuredAttrs, we get an error about nix not being allowed to refer to store paths. I tracked this down to tests/nixos/functional/common.nix

      system.extraDependencies = [
        (inputDerivation config.nix.package)
      ];

The inputDerivation function is meant to strip disallowedReferences

  # FIXME (roberth) reference issue
  inputDerivation =
    pkg:
    (pkg.overrideAttrs (o: {
      disallowedReferences = [ ];
    })).inputDerivation;

It seems like this is no longer working. I am also seeing

structuredAttrs is incompatible with {dis,}allowed{References,Requisites} which seems possibly related, but doesn't seem to be triggering, as I'm not seeing those warnings.

Things I haven't been able to figure out:

1. Why are we adding this to extraDependencies?
2. Where does disallowedReferences get set to non-empty value to begin with?

[Radvendii]

This update also seems to make clangd dysfunctional. Still investingating...

[Radvendii]

I can reproduce the __structuredAttrs allowedReferences error with the following:

(pkgs.hello.overrideAttrs {
  __structuredAttrs = true;
}).inputDerivation

This complains about the output not being allowed to refer to output paths.

I was suspicious of allowedReferences = null; in the implementation of inputDerivation, so I tried

let 
  __structuredAttrs = true;
in
  derivation ({
    inherit __structuredAttrs;
    system = "x86_64-linux";

    name = "test";
    outputs = [ "out" ];
    builder = pkgs.stdenv.shell;
    args = [
      "-c"
      ''
        out="${placeholder "out"}"
        echo "$out" > $out
      ''
    ];
  } // (
      let
        sharedOutputChecks = {
          allowedReferences = null;
        };
      in
      if __structuredAttrs then
        {
          outputChecks.out = sharedOutputChecks;
        }
      else
        sharedOutputChecks
    )
  )

And it does give the same error!

...But also it gives the same error when __structuredAttrs = false;, which hello.inputDerivation does not.

[edolstra]

Created a Hydra jobset for this: https://hydra.nixos.org/jobset/nix/pr-14688