Update index.md

Author: DanieleFena

content/actions/concepts/index.md

@@ -1,4 +1,4 @@
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 title: Concepts for GitHub Actions
 shortTitle: Concepts
 intro: "Learn the core concepts that you'll need to understand GitHub Actions."
@@ -13,4 +13,4 @@ children:
   - /security
   - /use-cases
   - /about-github-actions-metrics
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