Fix broken link in Rubocop message
What does this MR do and why?
Fix broken link in Rubocop message
The page at https://docs.gitlab.com/ee/development/uploads.html no longer exists, with upload docs having been moved into https://gitlab.com/gitlab-org/gitlab/-/tree/master/doc/development/uploads.
This MR updates the Rubocop guidance to point to the new location.