fix(steamos-update): Use double quotes to prevent potential globbing …

…and word splitting

system_files/deck/shared/usr/bin/steamos-update

@@ -68,7 +68,7 @@ if command -v ublue-update > /dev/null; then
     # Check if upgrade failed
     UPGRADE_CHECK=$(cat /tmp/upgrade-check)
     rm /tmp/upgrade-check
-    if [ ${UPGRADE_CHECK} -eq 0 ]; then
+    if [ "${UPGRADE_CHECK}" -eq 0 ]; then
       touch /tmp/upgrade-installed
     else
       exit 0 # Upgrade failed