ci: avoid qemu on local runners

.github/workflows/docker.yml

@@ -19,7 +19,18 @@ jobs:
     steps:
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
 
+      - name: Select Docker platforms
+        id: docker-platforms
+        shell: bash
+        run: |
+          if [ "${ACT:-}" = "true" ] || [ "${GITEA_ACTIONS:-}" = "true" ]; then
+            echo "platforms=linux/amd64" >> "$GITHUB_OUTPUT"
+          else
+            echo "platforms=linux/amd64,linux/arm64" >> "$GITHUB_OUTPUT"
+          fi
+
       - name: Set up QEMU
+        if: ${{ steps.docker-platforms.outputs.platforms != 'linux/amd64' }}
         uses: docker/setup-qemu-action@06116385d9baf250c9f4dcb4858b16962ea869c3 # v4
 
       - name: Set up Docker Buildx
@@ -31,7 +42,7 @@ jobs:
         uses: docker/build-push-action@f9f3042f7e2789586610d6e8b85c8f03e5195baf # v7
         with:
           context: .
-          platforms: linux/amd64,linux/arm64
+          platforms: ${{ steps.docker-platforms.outputs.platforms }}
           push: false
           build-args: |
             GIT_SHA=${{ github.sha }}