Do you already have the connector installed? (We don't QA our Git/Github connector on GitLab, however we do have reports that it will work)
If you already have the connector installed, then you'll link it with your commit message. Some examples are:
Fixed DE1987 by changing preamble paragraph 3
Test commit msg with multiple artifacts Fixed DE9 Closed DE8
Then, when the connector looks for updates it will detect that specific work items were mentioned and create those links. Additionally, if you have UpdateArtifactState set in the config file, it will change the state to the one mentioned in your commit message.