Revert "gitlab-ci.yml: remove git pull, blocking when git.openrobots.org is down"

This reverts commit 7dab533d.

rainboard/templates/rainboard/gitlab-ci.yml

@@ -14,6 +14,7 @@ cache:
   script:
     - mkdir -p ccache
     - cd /root/robotpkg/{{ robotpkg.category }}
+    - git pull
 {% if robotpkg.without_py %}    - cd {{ robotpkg.without_py }}
     - make checkout MASTER_REPOSITORY="git ${CI_PROJECT_DIR}/.git"
     - cd ..