Update Dockerfile - non-existent buildx version

[asaf400]

The download URL for the specified buildx version in the current Dockerfile (v0.13.2) was either removed at some point, or never existed..

The full 'default' URL is therefore broken: https://github.com/docker/buildx/releases/download/v0.13.2/buildx-v0.13.2.linux-amd64

while newer versions work:
https://github.com/docker/buildx/releases/download/v0.16.0/buildx-v0.16.0.linux-amd64

The change is UNTESTED, but I've looked through the release notes, and there only noticeable changes, but no breaking changes..

evidence of errors:

 > [build 6/6] RUN export RUNNER_ARCH=amd64     && if [ "$RUNNER_ARCH" = "amd64" ]; then export DOCKER_ARCH=x86_64 ; fi     && if [ "$RUNNER_ARCH" = "arm64" ]; then export DOCKER_ARCH=aarch64 ; fi     && curl -fLo docker.tgz https://download.docker.com/linux/static/stable/${DOCKER_ARCH}/docker-25.0.5.tgz     && tar zxvf docker.tgz     && rm -rf docker.tgz     && mkdir -p /usr/local/lib/docker/cli-plugins     && curl -fLo /usr/local/lib/docker/cli-plugins/docker-buildx         "https://github.com/docker/buildx/releases/download/v0.13.2/buildx-v0.13.2.linux-amd64"     && chmod +x /usr/local/lib/docker/cli-plugins/docker-buildx:
0.433   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
0.433                                  Dload  Upload   Total   Spent    Left  Speed
100 68.2M  100 68.2M    0     0  18.0M      0  0:00:03  0:00:03 --:--:-- 18.0M
16.83 curl: (22) The requested URL returned error: 404