fix(nginxproxymanager): reset PWD before certbot update to avoid deleted cwd

After building OpenResty, the script does cd /opt/openresty followed by
rm -rf /opt/openresty, leaving $PWD pointing to a deleted directory.
When pip runs in the certbot block, the subprocess inherits the invalid
PWD and fails with OSError: No such file or directory.

Add cd /root before the certbot block to reset to a valid directory.

Closes #13240

ct/nginxproxymanager.sh

@@ -102,6 +102,7 @@ EOF
     msg_ok "Built OpenResty"
   fi
 
+  cd /root
   if [ -d /opt/certbot ]; then
     msg_info "Updating Certbot"
     $STD /opt/certbot/bin/pip install --upgrade pip setuptools wheel