Bump docker/build-push-action from 3 to 4 (#27)

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](https://github.com/docker/build-push-action/compare/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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/container.yml

@@ -61,7 +61,7 @@ jobs:
       # this only builds the amd64 version of the image, which is fine as that's
       # all that is needed to test the container on Github Actions' build servers (which are running amd64 CPUs)
       - name: Build container image to test
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v4
         with:
           load: true # this is important, as this tells build-push-action to save the container to the local docker daemon
           build-args: |
@@ -94,7 +94,7 @@ jobs:
       # won't be rebuilt since the local docker daemon has that still cached
       - name: Push container image to registry
         if: inputs.do_upload
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v4
         with:
           platforms: linux/amd64,linux/arm/v7,linux/arm64/v8,linux/ppc64le,linux/s390x
           push: true