title: Map an environment variable in Github Actions
body: <p>I created a GitHub Actions Job with a strategy matrix that creates a set of environment variables.
  One of them is <code>machine_architecture</code> which is either 32 or 64. </p>
  
  <p>In most steps I can use it directly i.e. via <code>${{ machine_architecture }}</code>. 
  But some steps requires strings like 'i386' vs 'x86_64'. Is there an easy way in github actions to create a map-object that I can use in expressions like:</p>
  
  <pre><code>map_object = { 32: "i386", 64: 'x86_64' }
  ...
  ${{ map_object[machine_architecture] }}
  </code></pre>
  
  <p>If not, what is the idiomatic way in github actions to solve that problem?</p>
  
  <p>PS: I am aware, that I can <a href="https://help.github.com/en/actions/reference/development-tools-for-github-actions#set-an-environment-variable-set-env" rel="noreferrer">set environment variables in steps</a>, but the problem is, that these variables are only available for the following steps (i.e. not for usage in "run-on:" tag)</p>