The :required key is required is action.yml

* See https://help.github.com/en/actions/automating-your-workflow-with-github-actions/metadata-syntax-for-github-actions

Author: eregon

action.yml

@@ -7,6 +7,7 @@ branding:
 inputs:
   ruby-version:
     description: 'Engine and version to use, see the syntax in the README. Reads from .ruby-version if unset.'
+    required: false
     default: '.ruby-version'
 outputs:
   ruby-prefix: