Use arm64 runner for arm64 build

.github/workflows/container-trafficserver-alpine.yml

@@ -42,7 +42,7 @@ jobs:
       matrix:
         platform: [ 'amd64', 'arm64' ]
     if: ${{ github.repository_owner == 'apache' || github.event_name == 'workflow_dispatch' }}
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.toolchain == 'nightly' && ["self-hosted", "asf-arm"] || 'ubuntu-latest' }}
     steps:
       - name: Checkout repo
         uses: actions/checkout@master
@@ -66,14 +66,6 @@ jobs:
         run: cp .env '${{ github.env }}'
       - name: Set image name
         run: echo 'IMAGE_NAME=${{ env.CONTAINER }}:${{ env.ATS_VERSION }}-${{ matrix.platform }}' >> '${{ github.env }}'
-      - name: Install aarch64 emulator
-        if: ${{ env.SHOULD_RUN == '1' && matrix.platform == 'arm64' }}
-        run: docker run --rm --privileged tonistiigi/binfmt:qemu-v6.2.0 --install arm64
-      - name: Make a Docker Buildx builder
-        if: ${{ env.SHOULD_RUN == '1' && matrix.platform == 'arm64' }}
-        run: docker buildx create --name arm64-builder --use
-        # The push can be split into a separate command once docker can store
-        # multi-architecture images (docker/roadmap#371).
       - name: Build ${{ env.IMAGE_NAME }}
         if: ${{ env.SHOULD_RUN == '1' }}
         working-directory: .github/containers/trafficserver-alpine