[docker] use arm64 runner instead of qemu (openthread#11220)

.github/workflows/docker.yml

@@ -46,13 +46,18 @@ permissions:  # added using https://github.com/step-security/secure-workflows
 jobs:
 
   buildx:
-    name: buildx-${{ matrix.docker_name }}
-    runs-on: ubuntu-24.04
+    name: buildx-${{ matrix.docker_name }}-${{ matrix.arch }}
+    runs-on: ${{ matrix.runner }}
     strategy:
       fail-fast: false
       matrix:
         include:
           - docker_name: environment
+            arch: amd64
+            runner: ubuntu-24.04
+          - docker_name: environment
+            arch: arm64
+            runner: ubuntu-24.04-arm
     steps:
     - name: Harden Runner
       uses: step-security/harden-runner@0080882f6c36860b6ba35c610c98ce87d4e2f26f # v2.10.2
@@ -71,7 +76,7 @@ jobs:
       run: |
         DOCKER_IMAGE=openthread/${{ matrix.docker_name }}
         DOCKER_FILE=etc/docker/${{ matrix.docker_name }}/Dockerfile
-        DOCKER_PLATFORMS=linux/amd64,linux/arm64
+        DOCKER_PLATFORMS=linux/${{ matrix.arch }}
         VERSION=latest
 
         TAGS="--tag ${DOCKER_IMAGE}:${VERSION}"
@@ -85,11 +90,6 @@ jobs:
           --build-arg VCS_REF=${GITHUB_SHA::8} \
           ${TAGS} --file ${DOCKER_FILE} ." >> $GITHUB_OUTPUT
 
-    - name: Set up QEMU
-      uses: docker/setup-qemu-action@v3
-      with:
-        image: tonistiigi/binfmt:qemu-v8.1.5
-
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@6524bf65af31da8d45b59e8c27de4bd072b392f5 # v3.8.0