replace renku save by git push to update submodule in .gitlab-ci.yml

.gitlab-ci.yml

@@ -47,7 +47,8 @@ update_jupytext:
     git submodule update --remote
   after_script:
     - cd /tmp/${CI_COMMIT_SHORT_SHA}
-    - renku save -m "sync jupytext@$(git submodule status | cut -c2-9)"
+    - git commit -m "sync jupytext@$(git submodule status | cut -c2-9)"
+    - git push