build(deps): bump cachix/cachix-action from v6 to v8 (#4)

Bumps [cachix/cachix-action](https://github.com/cachix/cachix-action) from v6 to v8.
- [Release notes](https://github.com/cachix/cachix-action/releases)
- [Commits](https://github.com/cachix/cachix-action/compare/v6...6e4751ed42b22f60165d3f266cfa4cce66ae406d)

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

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

.github/workflows/build.yml

@@ -44,7 +44,7 @@ jobs:
     - name: Show nixpkgs version
       run: nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
     - name: Setup cachix
-      uses: cachix/cachix-action@v6
+      uses: cachix/cachix-action@v8
       if: ${{ matrix.cachixName != '<YOUR_CACHIX_NAME>' }}
       with:
         name: ${{ matrix.cachixName }}