build(deps): bump docker/build-push-action from 3 to 4

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 3 to 4.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v3...v4)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/docker.yml

@@ -20,15 +20,15 @@ jobs:
       # https://github.com/docker/setup-buildx-action#usage
       - uses: docker/setup-buildx-action@v2
       # https://github.com/docker/build-push-action#usage
-      - uses: docker/build-push-action@v3
+      - uses: docker/build-push-action@v4
         with:
           push: true
           file: Dockerfile_django
           tags: |
             ghcr.io/${{ github.repository }}-django:latest
           cache-from: type=gha
           cache-to: type=gha,mode=max
-      - uses: docker/build-push-action@v3
+      - uses: docker/build-push-action@v4
         with:
           push: true
           file: Dockerfile_static