Bump actions/checkout from 4 to 6

.github/workflows/check-base-image-update.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Check if update available
         id: check

.github/workflows/docker-buildx.yaml

@@ -27,7 +27,7 @@ jobs:
       id-token: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Get version
         id: pwsh_version

.github/workflows/get-latest-release.yaml

@@ -19,7 +19,7 @@ jobs:
             📚 Repository: [ ${{ github.repository }} ](https://github.com/${{ github.repository }})
 
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           # Have to use custom PAT, because commits created with GITHUB_TOKEN will not trigger CI
           # See: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#using-the-github_token-in-a-workflow

.github/workflows/keep-alive.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Ping
         run: echo "Keep-Alive workflow run on $(date)"