I had originally started out using a single GitLab server configuration in Manage Jenkins with an SSH Key. I then tried to add a new GitLab Personal Access Token from within the job creation screen and it didn't show up after hitting Save. Next, I tried to create a GitLab Personal Access Token from the main Credentials screen. It still did not show up in the job configuration. 

I can see all of the credentials in the Credentials plugin screens. However, it appears that the GitLab configuration only wants to show the SSH Key credential. Perhaps the server configuration somehow gets locked to a protocol? If that's the case, that might not be great from a security perspective since it would seem that job configuration might affect the whole Jenkins server configuration.