commands doesn't work when both `package` and `command` are set.

[landure]

Describe the bug

when describing a command with both package and command set, the package option is preferred to the command option.

This means that the command is not created with the expected name even if the name appears in the menu.

To Reproduce

Steps to reproduce the behavior:

        devshells.default.commands = [
          {
            name = "nil-diagnostics";
            command = ''
              shopt -s globstar
              ${getExe pkgs.nil} diagnostics ./**/*.nix
            '';
            package = pkgs.nil;
            category = "lint";
          }
        ];

The command appears in the menu, but nil-diagnostics isn't created.

Expected behavior

When both package and command are set, either:

1. display an error that it's one or the other.
2. create the command script, AND add both the command and package to the develop shell.

System information

nix --version
nix (Nix) 2.28.4

Additional context

devshell installed using flake parts.