make-update isn't as destructive as it once was. It should be safe to run as long as the developer is fixes any weird merge conflicts after stash pop.
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