[ci] Fix error in build-docker.yml (#116)

Author: JSUYA

.github/workflows/build-docker.yml

@@ -20,12 +20,12 @@ jobs:
           wget -q ${REPO_URL}/${BUILD_ID}/images/standard/${IMAGE}/${BUILD_ID}_${IMAGE}.tar.gz
           tar -zxf ${BUILD_ID}_${IMAGE}.tar.gz
           mkdir rootfs
+          sudo mount rootfs.img rootfs
 
           # TODO(jsuya) : vulkan-loader is not included in the image binary.
           wget -q ${REPO_URL}/${BUILD_ID}/repos/standard/packages/armv7l/vulkan-loader-1.3.208-0.armv7l.rpm
-          rpm2cpio vulkan-loader-1.3.208-0.armv7l.rpm | cpio -idmv -D rootfs
+          rpm2cpio vulkan-loader-1.3.208-0.armv7l.rpm | sudo cpio -idmv -D rootfs
 
-          sudo mount rootfs.img rootfs
           sudo tar -cC rootfs . | docker import - ghcr.io/${{ github.repository_owner }}/${IMAGE}
           sudo umount rootfs
           docker push ghcr.io/${{ github.repository_owner }}/${IMAGE}:latest