What does this MR do?
In this we make sure we properly link to a forked project if it was already forked to a certain namespace.
Why was this MR needed?
In https://canary.gitlab.com/gitlab-org/gitlab-ce/commit/193bc5268676fd2a639b6c0f9d4be3ba2d8f2086 we updated the link to use
POST which is required when triggering the new fork, but not when linking to an existing project.
Does this MR meet the acceptance criteria?
Changelog entry added, if necessary
Tests added for this feature/bug
Has been reviewed by Frontend