Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/hassfest.yaml

@@ -10,5 +10,5 @@ jobs:
   hassfest_custom:
     runs-on: "ubuntu-latest"
     steps:
-      - uses: "actions/checkout@v5.0.1"
+      - uses: "actions/checkout@v6.0.0"
       - uses: home-assistant/actions/hassfest@master

.github/workflows/validate.yaml

@@ -11,7 +11,7 @@ jobs:
   validate-hacs:
     runs-on: "ubuntu-latest"
     steps:
-      - uses: "actions/checkout@v5.0.1"
+      - uses: "actions/checkout@v6.0.0"
       - name: HACS validation
         uses: "hacs/action@main"
         with: