FIx linter with quotes

Author: AlenkaF

ci/scripts/python_wheel_unix_test.sh

@@ -107,10 +107,10 @@ is_free_threaded() {
 
 if [ "${CHECK_UNITTESTS}" == "ON" ]; then
   # Install testing dependencies
-  if [ $(is_free_threaded) = "ON" ]; then
+  if [ "$(is_free_threaded)" = "ON" ]; then
     echo "Free-threaded Python build detected"
     python -m pip install --no-build-isolation -r "${source_dir}/python/requirements-wheel-test-3.13t.txt"
-  elif [ $(is_free_threaded) = "OFF" ]; then
+  elif [ "$(is_free_threaded)" = "OFF" ]; then
     echo "Regular Python build detected"
     python -m pip install -U -r "${source_dir}/python/requirements-wheel-test.txt"
   fi