upgrade actions/checkout to v6.0.1

Author: fharper

.github/workflows/check-github-actions.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
 
       - name: Checkout this repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v6.0.1
 
       - name: Download actionlint
         id: get_actionlint