chore(deps): bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4...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>

.github/workflows/docker-publish.yml

@@ -24,7 +24,7 @@ jobs:
       cancel-in-progress: false
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up QEMU (for multi-arch builds)
         uses: docker/setup-qemu-action@v3

.github/workflows/pr-unit-tests.yml

@@ -23,13 +23,13 @@ jobs:
         working-directory: .
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         continue-on-error: true
         id: checkout_https
 
       - name: Checkout repository via SSH (fallback)
         if: steps.checkout_https.outcome == 'failure'
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           ssh-key: ${{ secrets.SSH_PRIVATE_KEY }}
           ssh-strict: false