Follow #48
Empty steps are invalid, so remove them when decoding `Job` from YAML.
Reviewed-on: https://gitea.com/gitea/act/pulls/49
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-committed-by: Zettat123 <zettat123@gmail.com>
