When updating from https://github.com/cachix/install-nix-action/releases/tag/v30 to https://github.com/cachix/install-nix-action/releases/tag/v31, I'm starting to see many, many instances of the following in our GitHub Workflow logs:

warning: Nix search path entry '/home/runner/.nix-defexpr/channels' does not exist, ignoring

Our workflows look basically like this:

      - uses: cachix/install-nix-action@v30

      - uses: cachix/cachix-action@v16
        with:
          name: our-cachix-name
          authToken: "..."

...

      - name: cabal build in nix-shell
        run: |
          nix-shell --verbose --command 'cabal build all'

I'm seeing the above warning lines when running nix-shell, during the Nix evaluation phase. The message repeats over and over, many times.

I've also tried specifying a with: {nix-path: "nixpkgs=channel:nixos-unstable"} to the cachix/install-nix-action@v31, but that didn't seem to make any difference.

My guess is that this problem is related to NixOS/nix#11079, but I didn't try to confirm this. I don't really understand exactly what is going on in that issue, or the interactions between the NIX_PATH env var, and the nix-path setting in nix.conf.