Bump actions/checkout to v6

Author: pnbruckner

.github/workflows/validate.yml

@@ -10,7 +10,7 @@ jobs:
     name: With hassfest
     steps:
     - name: 📥 Checkout the repository
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: 🏃 Hassfest validation
       uses: "home-assistant/actions/hassfest@master"