ci: Retry submodule sync 2 more times before failing

.gitlab-ci.yml

@@ -731,6 +731,7 @@ check_submodule_sync:
   <<: *check_job_template
   variables:
     GIT_STRATEGY: clone
+  retry: 2
   script:
     # check if all submodules are correctly synced to public repostory
     - git submodule update --init --recursive