fix(updater): fix ignored variable name in read

I used _ which is a convention in other languages, but in shell scripting
$_ is a special variable set by the shell, and in Zsh versions older than
5.0.6 it complains for being a `read-only variable`.

Fixes #9482

tools/upgrade.sh

@@ -33,7 +33,7 @@ if [ -t 1 ]; then
 fi
 
 # Update upstream remote to ohmyzsh org
-git remote -v | while read remote url _; do
+git remote -v | while read remote url extra; do
   case "$url" in
   https://github.com/robbyrussell/oh-my-zsh(|.git))
     git remote set-url "$remote" "https://github.com/ohmyzsh/ohmyzsh.git"