fix(scripts): typo in publish.sh buildx error ('sudosudo')

${SUDO:+...}${SUDO:-...} is not the right ternary — ${SUDO:+x} expands
to 'x' when SUDO is non-empty AND ${SUDO:-y} expands to 'y' when SUDO
is empty, but they're not exclusive substitutions of the same variable
in this context, so 'sudo' (the value of $SUDO when set) leaked into
the output as 'sudosudo'. Replaced with an explicit if/else.

scripts/publish.sh

@@ -62,9 +62,10 @@ ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 PLATFORMS="${CM_IMAGE_PLATFORMS:-linux/amd64}"
 
 if ! "${DOCKER[@]}" buildx version >/dev/null 2>&1; then
+  RUNNER="$([[ -n "${SUDO}" ]] && echo "root via sudo" || echo "current user")"
   cat <<EOF >&2
 Docker Buildx isn't reachable as the user this script runs docker as
-(${SUDO:+root via sudo}${SUDO:-current user}).
+(${RUNNER}).
 
 Likely cause: buildx is installed at the per-user path
 ~/.docker/cli-plugins/docker-buildx, which sudo doesn't see.