Sometimes you can get stuck in a loop where git stash pop preserves the stash commit. Dropping that commit if it's a STASH commit after an update is totally fine.
Adding the "common" subtree as your .gitlab folder
# Add the subtree as a remote
git subtree add --prefix .gitlab git@gitlab.ducoterra.net:services/common.git main --squash
# Now you can run the following to update
make make-update