Move test into matrix to reuse code

[whs-dot-hk]

This piece of code is the same, we could reuse it in tests

    strategy:
      matrix:
        os: [ubuntu-latest]
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v2.3.4
      - uses: nixbuild/nix-quick-install-action@v9
        with:
          nix_conf: |
            allowed-uris = https://github.com/NixOS/nixpkgs https://github.com/input-output-hk https://github.com/NixOS/nixpkgs-channels
            trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= iohk.cachix.org-1:DpRUyj7h7V830dp/i6Nti+NEO2/nhblbov/8MW7Rqoo= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
            substituters = https://hydra.iohk.io https://iohk.cachix.org https://cache.nixos.org/