The branch does not exist in dist-git, only in PDC. That is because a hook is active to prevent accidental branches.

There are instructions on how to create that branch in dist-git listed at https://pagure.io/releng/fedora-scm-requests/issue/50274#comment-834375

If you cannot reach the settings, you might need to coordinate that with me (main admin). I've disabled the hook for now and will enable it once the branch is pushed.

That seems to have done the trick, thanks!