Bump actions/checkout from 3 to 4 [skip cd] (#12)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/docker-image.yml

@@ -18,7 +18,7 @@ jobs:
     outputs:
       docker-image: ${{ steps.generate-build-variables.outputs.docker-image }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0 # checkout everything.
 
@@ -65,7 +65,7 @@ jobs:
     if: github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: aquasecurity/trivy-action@master
         with:
           image-ref: 'docker.io/epages/${{ github.event.repository.name }}:${{ needs.build.outputs.docker-image }}'