dockerTools.buildImage.runAsRoot: preserve layers ordering at image unpacking

This patch preserves the ordering of layers of a parent image when the
image is unpacked.

Fixes #55290

pkgs/build-support/docker/default.nix

@@ -200,7 +200,7 @@ rec {
       # Unpack all of the parent layers into the image.
       lowerdir=""
       extractionID=0
-      for layerTar in $(cat layer-list); do
+      for layerTar in $(tac layer-list); do
         echo "Unpacking layer $layerTar"
         extractionID=$((extractionID + 1))