Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/build-docker.yml

@@ -15,7 +15,7 @@ jobs:
     name: Build Docker Image
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install buildx
       uses: docker/setup-buildx-action@v3
     - name: Login to Docker

.github/workflows/run-tests.yml

@@ -38,7 +38,7 @@ jobs:
         if: ${{ contains(matrix.container, 'slim') }}
         run: apt-get -y update && apt-get -y install git curl
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Fix Git-Permissions
         run: git config --global --add safe.directory "$GITHUB_WORKSPACE"
       - name: Test