That’s probably because it’s not detecting spam in the post at all, but instead it’s flagged your account as a spammer. The GitLab docs on spam management heavily imply that’s how their system works, and if that’s the case then the contents what you’re trying to post are immaterial.
You’ll probably need a local Administrator to go into the Admin Area for the instance (see second link) and remove any outstanding reports for your account, to unrestrict you from posting.
No, I guarantee it’s nothing to do with that. Something (either an algorithm or a human) must’ve flagged some previous activity of yours as spam. Perhaps erroneously! But now that you’re branded “a spammer” in their system, you’re in spammer-jail unless someone overrides that report.
You could create a new account with a different email address, I suppose, but that seems like overkill. I’d try to get it cleared up with your current account, first. Not sure how you’d go about contacting GNOME GitLab admins, though, since you obviously can’t open an issue about this… was hoping this would get noticed by or referred to someone with admin rights, but doesn’t seem that way.
The #sysadmin channel on IRC or, #sysadmin:gnome.org on Matrix, is usually where the GNOME infrastructure admins can be found. They also read topics in this category on Discourse.