chore(deps): bump cachix/install-nix-action from 20 to 21 (#1)

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 20 to 21.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v20...v21)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/nix-build.yml

@@ -8,7 +8,7 @@ jobs:
     name: Nix checks
     steps:
     - uses: actions/checkout@v3
-    - uses: cachix/install-nix-action@v20
+    - uses: cachix/install-nix-action@v21
     - uses: cachix/cachix-action@v12
       with:
         name: neorocks
@@ -28,7 +28,7 @@ jobs:
           - .#devShells.x86_64-linux.default
     steps:
     - uses: actions/checkout@v3
-    - uses: cachix/install-nix-action@v20
+    - uses: cachix/install-nix-action@v21
     - uses: cachix/cachix-action@v12
       with:
         name: neorocks
@@ -41,7 +41,7 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@v21
       - uses: cachix/cachix-action@v12
         with:
           name: neorocks