chore(deps): bump cachix/install-nix-action from 30 to 31

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 30 to 31.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](https://github.com/cachix/install-nix-action/compare/v30...v31)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - run: nix profile install nixpkgs#devenv
       - name: Build
         run: devenv shell -- pnpm build

.github/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - name: Test public cache
         uses: ./
         with:
@@ -31,7 +31,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - name: Test public cache no signing key
         uses: ./
         with:
@@ -49,7 +49,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - name: Test private cache
         uses: ./
         with:
@@ -66,7 +66,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - id: paths
         run: |
           paths=$(nix-instantiate test.nix | tr '\n' ' ')
@@ -85,7 +85,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - name: Test private cache
         uses: ./
         with:
@@ -114,7 +114,7 @@ jobs:
           chmod +x ./nar-toolbox-${{ matrix.system }}
           ./nar-toolbox-${{ matrix.system }} serve https://cache.nixos.org &
 
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
         with:
           install_url: https://hydra.nixos.org/job/nix/master/installerScript/latest-finished/download/1/install
           install_options: "--tarball-url-prefix http://localhost:8080"