Basic fix to allow for reusable workflows.

[hanleym]

Currently, steps defaults to [] (unhelpful) and runs-on is always set. This prevents using reusable workflows where job has a uses attribute instead of steps. (GitHub doesn't allow both to be set.) This fix allows steps to be null (not in the final yaml) and runs-on is only set if steps is set.

[nialov]

Thanks for the PR! Can you

1. git rebase -i origin/master && git push --force-with-lease. I changed the GitHub action config on master to run on pull requests.
2. Run nix develop -c pre-commit run --all-files. There was one file that nixfmt-rfc-style changes.

➜ nix flake check
warning: unknown flake output 'self'
warning: unknown flake output 'actions-nix'
trace: Obsolete option `defaults' is used. It was renamed to `defaultValues'.
error: builder for '/nix/store/29kbsshc751fxw50yj969v8f1hff4ak1-pre-commit-run.drv' failed with exit code 1;
       last 25 log lines:
       > no configure script, doing nothing
       > Running phase: buildPhase
       > Running: $ pre-commit run --all-files
       > deadnix..................................................................Passed
       > nixfmt-rfc-style.........................................................Failed
       > - hook id: nixfmt-rfc-style
       > - files were modified by this hook
       > render-workflows.........................................................Passed
       > statix...................................................................Passed
       > trim-trailing-whitespace.................................................Passed
       > diff --git a/nix/flake-modules/actions-nix/ci.nix b/nix/flake-modules/actions-nix/ci.nix
       > index 49fa923..c0971b4 100644
       > --- a/nix/flake-modules/actions-nix/ci.nix
       > +++ b/nix/flake-modules/actions-nix/ci.nix
       > @@ -27,7 +27,9 @@ let
       >        };
       >      };
       >    };
       > -  jobModule = { config, ... }: {
       > +  jobModule =
       > +    { config, ... }:
       > +    {
       >        freeformType = lib.types.attrs;
       >        options = {
       >          runs-on = mkEmptyDescriptionOption {
       For full logs, run:
         nix log /nix/store/29kbsshc751fxw50yj969v8f1hff4ak1-pre-commit-run.drv

Will merge after these!

[nialov]

I am also interested in an example repository where you use this if you have one public? I do not think I have used jobs.<job_id>.uses myself previously (even though code minimization is my goal 😄 ).

[nialov]

Merged in #29