fix: small bug in install script

install_spack_env.sh

@@ -130,7 +130,7 @@ spack-python -c "exit(not len(spack.environment.active_environment().uninstalled
     else
         echo "Updating of the source cache disabled."
     fi
-    if [ $ret -ne 0 ]; then
+    if [ "$ret" -ne 0 ]; then
         (exit $ret)
     fi
 )