chore(deps): bump docker/build-push-action from 4 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 4 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v4...v6)

---
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/test_publish.yml

@@ -224,7 +224,7 @@ jobs:
           username: ${{ secrets.RENKU_DOCKER_USERNAME }}
           password: ${{ secrets.RENKU_DOCKER_PASSWORD }}
       - name: Build and push data services
-        uses: docker/build-push-action@v4
+        uses: docker/build-push-action@v6
         with:
           context: .
           file: ./projects/renku_data_service/Dockerfile
@@ -249,7 +249,7 @@ jobs:
             type=semver,pattern={{major}}.{{minor}}
             type=sha
       - name: Build and push background jobs
-        uses: docker/build-push-action@v4
+        uses: docker/build-push-action@v6
         with:
           context: .
           file: ./projects/background_jobs/Dockerfile
@@ -274,7 +274,7 @@ jobs:
             type=semver,pattern={{major}}.{{minor}}
             type=sha
       - name: Build and push secrets image
-        uses: docker/build-push-action@v4
+        uses: docker/build-push-action@v6
         with:
           context: .
           file: ./projects/secrets_storage/Dockerfile