borg.sh: Fix name of a variable

In [1: e27463e] the local variable `remote_url' was renamed to `url'
but one instance was overlooked.

1: 2022-11-25 e27463e
   Improve bootstrapping

Author: Thaodan

borg.sh

@@ -97,7 +97,7 @@ clone () {
                 echo "Cloning $path from $remote ($url)"
 
                 mkdir -p "$modsdir"
-                if git clone "$remote_url" "$path" \
+                if git clone "$url" "$path" \
                        --separate-git-dir "$modsdir/$name"
                 then
                     git remote rename origin "$remote"