Bump actions/checkout from 3 to 4 (#19)

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/dockerpush.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-20.04
     if: github.event_name == 'pull_request'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Run tests
         run: |
           if [ -f docker-compose.test.yml ]; then
@@ -35,7 +35,7 @@ jobs:
     runs-on: ubuntu-20.04
     if: github.event_name == 'push'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Login to Docker Hub
         uses: docker/login-action@v2
         with: