Change clone branch to main

.gitlab-ci.yml

 before_script:
   - apt update >/dev/null && apt install -y git >/dev/null
-  - git clone --depth=1 --branch ros2 https://forgemia.inra.fr/vincent.rousseau1/ros_gitlab_ci.git >/dev/null
+  - git clone --depth=1 --branch main https://forgemia.inra.fr/vincent.rousseau1/ros_gitlab_ci.git >/dev/null
 
 humble:build:
   image: ros:humble-ros-base