pin empy version in ros CI test

Author: CoolSpy3

.github/workflows/test_suite_linux.yml

@@ -160,7 +160,7 @@ jobs:
       run: |
         export WEBOTS_HOME=$PWD/artifact/webots
         export ROS_DISTRO=${{ matrix.ROS_DISTRO }}
-        python -m pip install rospkg catkin_pkg empy defusedxml netifaces
+        python -m pip install rospkg catkin_pkg empy==3.3.4 defusedxml netifaces
         Xvfb :99 &
         export DISPLAY=:99
         ./tests/ros.sh