Creating a Gitlab Trusted Publisher for an existing project gives 404

[sebastianw]

Describe the bug

Trying to create a trusted publisher for a Gitlab hosted project only returns a 404 error. This is a companion issue to #18986 where a pending publisher fails.

Expected behavior

A publisher is created.

To Reproduce

Go to a project publishing setting and try to add a Gitlab Trusted Publisher.

My Platform

MacOS 15.6.1 with Firefox 144.0.2
Additional context