build(deps): bump docker/build-push-action from 4 to 6 (#487)

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-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Author: dependabot[bot]

.github/workflows/docker.yml

@@ -28,13 +28,13 @@ jobs:
           password: ${{ secrets.DOCKER_ACCESS_TOKEN }}
 
       - name: Build and push docker image
-        uses: docker/build-push-action@v4
+        uses: docker/build-push-action@v6
         with:
           push: true
           tags: getyourguide/istio-config-validator:latest
 
       - name: Build and push istio-router-check
-        uses: docker/build-push-action@v4
+        uses: docker/build-push-action@v6
         with:
           pull: true
           file: hack/istio-router-check/Dockerfile