dynamically use a normal runner in a reusable workflow, for example ubuntu-latest or a group of runners

[jmirandasq]

I am trying to make a workflow work that can receive the name of a runner group through an input, but if nothing is received through the input, use the ubuntu-latest label. Is this possible? I come from azure devops and with expressions I could modify the yaml and I can't find how to do it on github.

pool: 
    ${{ if eq(parameters['agenteSiste'], 'none') }}:
      vmImage: ${{parameters.agenteAzure}}
    ${{ else }}:
      name: ${{parameters.agenteSiste}}

This is how I did it in Azure Pipelines