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/build-and-test.yml

@@ -35,7 +35,7 @@ jobs:
       # build unstable image used for test suite
       #
       - name: Build testing image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           cache-from: type=gha
           cache-to: type=gha,mode=max
@@ -75,7 +75,7 @@ jobs:
       - name: Build and push unstable
         if: ${{ github.event_name == 'release' || ((github.event_name == 'push' || github.event_name == 'schedule') && github.ref == 'refs/heads/master') }}
         id: docker_build
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./docker
           file: ./docker/Dockerfile
@@ -91,7 +91,7 @@ jobs:
         run: echo ::set-output name=tag::$(echo ${GITHUB_REF:10})
       - name: Build and push release
         if: ${{ github.event_name == 'release' }}
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./docker
           file: ./docker/Dockerfile