Fix Zephyr CI (#480)

Signed-off-by: Pablo Garrido <pablogs9@gmail.com>
(cherry picked from commit 0942f74)

config/zephyr/generic/create.sh

@@ -54,4 +54,7 @@ pushd $FW_TARGETDIR >/dev/null
     touch mcu_ws/uros/rcl/rcl_yaml_param_parser/COLCON_IGNORE
     touch mcu_ws/uros/rclc/rclc_examples/COLCON_IGNORE
 
+    # Workaround. Remove when https://github.com/sphinx-doc/sphinx/issues/10291 and https://github.com/micro-ROS/micro_ros_zephyr_module/runs/5714546662?check_suite_focus=true
+    pip3 install --upgrade Sphinx
+
 popd >/dev/null