Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build.yaml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: ESPHome
         uses: esphome/build-action@v7
         with: