fix: remove hardcoded ROS shell paths

src/mtran/test/test_cmake_preparation.sh

@@ -17,10 +17,10 @@ rsync -a \
   --exclude 'models/en_zh-Hans/' \
   "${root}/" "${fixture}/"
 
-# shellcheck disable=SC1091
-set +u
-source /opt/ros/humble/setup.bash
-set -u
+if [[ "${ROS_DISTRO:-}" != "humble" ]]; then
+  echo "ROS2 Humble environment must be sourced before running this test" >&2
+  exit 1
+fi
 
 if missing_output=$(cmake -S "${fixture}" -B "${fixture}/build-missing" 2>&1); then
   echo "CMake unexpectedly configured without prepared runtime files" >&2