Gitlab plugin refuses http URL

Hi,
I’m running my own on-premises GibLab instance, not visible to the Internet, and connect to it using a http:// scheme (i. e. not https).
When using the gitlab plugin, I seem to be unable to enter the URL - the " GitLab instance address" field keeps “correcting” it into a https URL.
How can I connect to my http GitLab instance?
Cheers,
@sarcarsten