This is a custom build of the standard Jenkins CI GitLab Plugin expecting GitLab HTTP remotes instead of GitLab SSH remotes.
There is an outstanding ticket #447 that describes this issue, but this has not yet been solved. Until then, you can use this build instead of the standard one.
To install, remove the existing GitLab Plugin, go to the Advanced tab in the plugin manager and upload the attached .hpi file. This should just work, but because this plugin has a different name from the standard version, there may be issues.