Move Nix options to common

infra/common/default.nix

@@ -16,6 +16,13 @@ in
   system.stateVersion = "24.05"; # do not change
   nixpkgs.hostPlatform = mkDefault "x86_64-linux";
 
+  ## This is just nice to have, but it is also particularly important for the
+  ## Forgejo CI runners because the Nix configuration in the actions is directly
+  ## taken from here.
+  nix.extraOptions = ''
+    experimental-features = nix-command flakes
+  '';
+
   environment.systemPackages = with pkgs; [
     (pkgs.vim_configurable.customize {
       name = "vim";

infra/vm02179/gitea-runner.nix

@@ -33,10 +33,4 @@
       };
     };
   };
-
-  ## The Nix configuration of the system influences the Nix configuration
-  ## in the workflow, and our workflows are often flake-based.
-  nix.extraOptions = ''
-    experimental-features = nix-command flakes
-  '';
 }

infra/vm02186/gitea-runner.nix

@@ -40,10 +40,4 @@
 
   ## For the Docker mode of the runner.
   virtualisation.docker.enable = true;
-
-  ## The Nix configuration of the system influences the Nix configuration
-  ## in the workflow, and our workflows are often flake-based.
-  nix.extraOptions = ''
-    experimental-features = nix-command flakes
-  '';
 }