message: [github-actions] build docker image for reference device
  This commit enhances the docker build test to use more options.
diff: @@ -45,9 +45,15 @@ jobs:
  strategy:
  matrix:
  include:
  - - build_args: ""
  + - image_tag: "latest"
  + build_args: ""
  push: yes
  - - build_args: "--build-arg OT_BACKBONE_CI=1"
  + - image_tag: "reference-device"
  + build_args: "--build-arg REFERENCE_DEVICE=1 --build-arg BACKBONE_ROUTER=1 --build-arg OTBR_OPTIONS='-DOT_DUA=ON -DOT_MLR=ON' --build-arg NAT64=0"
  + push: yes
  + - image_tag: "test"
  + build_args: "--build-arg REFERENCE_DEVICE=1 --build-arg BACKBONE_ROUTER=1 --build-arg OTBR_OPTIONS='-DOT_DUA=ON -DOT_MLR=ON' --build-arg OT_BACKBONE_CI=1"
  + push: no
  steps:
  - uses: actions/checkout@v2
  with:
  @@ -64,18 +70,18 @@ jobs:
  run: |
  DOCKER_IMAGE=openthread/otbr
  DOCKER_PLATFORMS=linux/amd64,linux/arm/v7,linux/arm64
  - VERSION=latest
  + VERSION=${{ matrix.image_tag }}
  TAGS="--tag ${DOCKER_IMAGE}:${VERSION}"
  echo ::set-output name=docker_image::${DOCKER_IMAGE}
  echo ::set-output name=version::${VERSION}
  - echo ::set-output name=buildx_args::--platform ${DOCKER_PLATFORMS} \
  + echo ::set-output name=buildx_args::"--platform ${DOCKER_PLATFORMS} \
  --build-arg VERSION=${VERSION} \
  --build-arg BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ') \
  --build-arg VCS_REF=${GITHUB_SHA::8} \
  ${{ matrix.build_args }} \
  - ${TAGS} --file etc/docker/Dockerfile .
  + ${TAGS} --file etc/docker/Dockerfile ."
  - name: Docker Buildx (build)
  run: |
  