add hydra.iohk.io binary cache

Author: garbas

.github/actions/nix-common-setup/action.yml

@@ -11,6 +11,10 @@ runs:
       uses: cachix/install-nix-action@v16
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
+        extra_nix_config: |
+          accept-flake-config = true
+          trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+          substituters = https://hydra.iohk.io https://cache.nixos.org/
 
     - uses: cachix/cachix-action@v10
       with: