This?

.forgejo/install-emacs/install-nix.sh

@@ -79,9 +79,11 @@ else
   # "fix" the following error when running nix*
   # error: the group 'nixbld' specified in 'build-users-group' does not exist
   add_config "build-users-group ="
-  mkdir -p /etc/nix
-  chmod 0755 /etc/nix
-  cp "$workdir/nix.conf" /etc/nix/nix.conf
+  apt-get update -qq
+  apt-get install -y sudo
+  sudo mkdir -p /etc/nix
+  sudo chmod 0755 /etc/nix
+  sudo cp "$workdir/nix.conf" /etc/nix/nix.conf
 fi
 
 if [[ -n "${INPUT_INSTALL_OPTIONS:-}" ]]; then