Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Set up Python
         uses: actions/setup-python@v5
         with:

.github/workflows/container_build.yml

@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Log in to the Container registry
         uses: docker/login-action@v3