Merge #11649: Revert "Remove unused variable in shell script"

fa0025dc3 Revert "Remove unused variable in shell script" (MarcoFalke)

Pull request description:

  This partially reverts commit ab8e8b97a3 (#10771), as the variable is still used. See for example #11394.

Tree-SHA512: 1788d5471e1399d4a15d287cd8c41979833524e31b8fe61af8a7d20c9777828460d61ab87885a228ba7ca919f1d08703f4cb182d5840eb863e2154b3cf8ff4e6

contrib/devtools/git-subtree-check.sh

@@ -48,6 +48,7 @@ if [ -z "$latest_squash" ]; then
 fi
 
 set $latest_squash
+old=$1
 rev=$2
 if [ "d$(git cat-file -t $rev 2>/dev/null)" != dcommit ]; then
     echo "ERROR: subtree commit $rev unavailable. Fetch/update the subtree repository" >&2