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?

This is the old way:

fork-error

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