Add fork error when the user already forked the project
What should be the behaviour when the user already forked the project in the [new fork form](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/53544)? This is the old way: ![fork-error](/uploads/de27dead52c52acc174e77c202a15520/fork-error.mov) This functionality was a requirement that existed in our old testing spec file > https://gitlab.com/gitlab-org/gitlab/-/blob/a8063e249382969ac1ddddcd2ecef88a6f0265d4/spec/features/projects/fork_spec.rb#L233
issue