build(deps): bump cachix/install-nix-action from 17 to 18

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 17 to 18.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v17...v18)

---
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

@@ -13,7 +13,7 @@ jobs:
       with:
           # Nix Flakes doesn't work on shallow clones
           fetch-depth: 0
-    - uses: cachix/install-nix-action@v17
+    - uses: cachix/install-nix-action@v18
     - name: List flake structure
       run: nix flake show
     - name: Run unit tests (flake)