Change acctest GitLab port to 8085

This changes the GitLab instance port from 8080 to 8085. The reason for this generally is that 8080 is a very widely used port and since we map it to localhost may conflict. More concretely is that the GitLab Configure Team who maintains this provider also maintains the GitLab Agent for Kubernetes which uses port 8080 as a default port for the local observability stack and thus conflicts for me all the time.