chore: move extraction of archive

Author: rjaegers

.devcontainer/cpp/Dockerfile

@@ -3,15 +3,20 @@ ARG DOCKER_VERSION=28.2.2
 FROM scratch AS downloader-amd64
 
 ADD --checksum=sha256:53dc06dc3f775282ddff93b2d0974bbe6480761018c61e7a797342a9c7f14e23 \
- https://download.docker.com/linux/static/stable/x86_64/docker-${DOCKER_VERSION}.tgz
+ https://download.docker.com/linux/static/stable/x86_64/docker-${DOCKER_VERSION}.tgz /docker.tgz
 
 FROM scratch AS downloader-arm64
 
 ADD --checksum=sha256:c9506628d1845c69230df3d87e2eedd7980caf8bd966f5e6a5d7a2364de42497 \
- https://download.docker.com/linux/static/stable/aarch64/docker-${DOCKER_VERSION}.tgz
+ https://download.docker.com/linux/static/stable/aarch64/docker-${DOCKER_VERSION}.tgz /docker.tgz
 
 FROM downloader-$TARGETARCH AS downloader
 
+FROM ubuntu:24.04@sha256:6015f66923d7afbc53558d7ccffd325d43b4e249f41a6e93eef074c9505d2233 AS extractor
+
+RUN --mount=from=downloader,target=/tmp \
+ tar xzf /tmp/docker.tgz -C /tmp
+
 FROM ubuntu:24.04@sha256:6015f66923d7afbc53558d7ccffd325d43b4e249f41a6e93eef074c9505d2233
 
 ARG BATS_VERSION=1.11.0
@@ -69,7 +74,7 @@ RUN mkdir /opt/gcc-arm-none-eabi \
 ENV PATH="$PATH:/opt/gcc-arm-none-eabi/bin"
 
 # Install docker-cli for Docker-from-Docker tools
-COPY --from=downloader /docker/docker/docker /usr/local/bin
+COPY --from=extractor /tmp/docker/docker /usr/local/bin
 
 # Install bats
 RUN batstmp="$(mktemp -d /tmp/bats-core-${BATS_VERSION}.XXXX)" \