ci: Remove explicit platform build option (#20)

Author: shrink

.github/workflows/build.yml

@@ -32,7 +32,6 @@ jobs:
           build-args: PHP=${{ matrix.php }}
           labels: "${{ steps.meta.outputs.labels }}"
           outputs: "type=tar,dest=${{ env.archive }}"
-          platforms: linux/amd64
           tags: "${{ steps.meta.outputs.tags }}"
       - name: Upload Docker Image as pipeline artifact
         uses: actions/upload-artifact@v2