update actions, switch nix installer, use lix

And use `nix profile install` with `--inputs-from` so `direnv` and
`nix-direnv` are also pinned.

.github/workflows/ci.yml

@@ -18,45 +18,40 @@ jobs:
 
     steps:
       - name: Sync repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Uninstall obstructive tools
         run: rm -rf "$HOME/.rustup" "$HOME/.cargo"
 
-      - name: Install Nix (with flakes and nix-command enabled)
-        uses: cachix/install-nix-action@v23
+      - name: Install Lix (with flakes and nix-command enabled)
+        uses: DeterminateSystems/nix-installer-action@v12
         with:
-          nix_path: nixpkgs=channel:nixos-unstable
+          source-url: https://install.lix.systems/lix/lix-installer-x86_64-linux
 
-          # Use a version of Nix that doesn't suffer from the following issues:
-          #
-          # * <https://github.com/NixOS/nix/issues/8443>
-          # * <https://github.com/NixOS/nix/issues/9052>
-          install_url: https://releases.nixos.org/nix/nix-2.15.2/install
-
-          # Add the `nix-community` cachix to speed up things that leverage it
-          extra_nix_config: |
+          extra-conf: |
+            # Add the `nix-community` cachix to speed up things that leverage it
             extra-substituters = https://nix-community.cachix.org
             extra-trusted-public-keys = nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs=
 
       - name: Pop/push Magic Nix Cache
-        uses: DeterminateSystems/magic-nix-cache-action@v2
+        uses: DeterminateSystems/magic-nix-cache-action@v7
 
       - name: Configure `nix-direnv`
         run: |
           echo 'source $HOME/.nix-profile/share/nix-direnv/direnvrc' > "$HOME/.direnvrc"
 
       - name: Install `direnv` and `nix-direnv`
-        run: nix-env -f "<nixpkgs>" -i direnv -i nix-direnv
+        run: |
+          nix profile install nixpkgs#direnv nixpkgs#nix-direnv --inputs-from .
 
       - name: Pop/push downloaded crate cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           key: downloaded-crates
           path: ~/.cargo
 
       - name: Pop/push compiled crate cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           key: compiled-crates-${{runner.os}}
           path: target