Update 2020-04-16-hassfest.md (#1717)

Author: jwillemsen

blog/2020-04-16-hassfest.md

@@ -28,7 +28,7 @@ To install it, follow these steps:
      validate:
        runs-on: "ubuntu-latest"
        steps:
-         - uses: "actions/checkout@v2"
+         - uses: "actions/checkout@v3"
          - uses: home-assistant/actions/hassfest@master
    ```