chore: synchronise get-docker.sh with upstream

get-docker.sh

@@ -99,7 +99,7 @@ set -e
 
 # Git commit from https://github.com/docker/docker-install when
 # the script was uploaded (Should only be modified by upload job):
-SCRIPT_COMMIT_SHA="02cb80d6c7d24c85a458ae31d166a6c535c7a37a"
+SCRIPT_COMMIT_SHA="5ce20f2eef3615d08fea941eda5a109e949e8ebf"
 
 # strip "v" prefix if present
 VERSION="${VERSION#v}"
@@ -634,7 +634,11 @@ do_install() {
 				if ! is_dry_run; then
 					set -x
 				fi
-				$sh_c "DEBIAN_FRONTEND=noninteractive apt-get -y -qq install $pkgs >/dev/null"
+				apt_flags="-y -qq"
+				if [ -n "$pkg_version" ]; then
+					apt_flags="$apt_flags --allow-downgrades"
+				fi
+				$sh_c "DEBIAN_FRONTEND=noninteractive apt-get $apt_flags install $pkgs >/dev/null"
 			)
 			if [ "$NO_AUTOSTART" != "1" ]; then
 				start_docker_daemon