build(deps): bump docker/build-push-action from 5 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 5 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v5...v6)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/push-build-test-on-push.yml

@@ -27,7 +27,7 @@ jobs:
           org.opencontainers.image.documentation=https://github.com/${{github.repository}}#readme
           org.opencontainers.image.licenses=MIT
     - name: build test image
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: .
         load: true
@@ -46,7 +46,7 @@ jobs:
         username: ${{ secrets.DOCKER_USERNAME }}
         password: ${{ secrets.DOCKER_PASSWORD }}
     - name: push to registry (unless pull request)
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       if: ${{ github.event_name != 'pull_request' && github.ref == 'refs/heads/main' }}
       with:
         context: .