Pass $CI_COMMIT_TAG as GITLAB_TAG to the CNG triggered pipelines

Signed-off-by: Rémy Coutable <remy@rymai.me>

scripts/trigger-build

@@ -140,6 +140,7 @@ module Trigger
         # Back-compatibility until https://gitlab.com/gitlab-org/build/CNG/merge_requests/189 is merged
         "GITLAB_#{edition}_VERSION" => ENV['CI_COMMIT_REF_NAME'],
         "GITLAB_VERSION" => ENV['CI_COMMIT_REF_NAME'],
+        "GITLAB_TAG" => ENV['CI_COMMIT_TAG'],
         "GITLAB_ASSETS_TAG" => ENV['CI_COMMIT_REF_SLUG'],
         "#{edition}_PIPELINE" => 'true'
       }