If an update to the project path fails validation, the unsaved
attributes would still be presented because the controller would fall
through and call `render` on the unsaved object. This resulted in the
wrong project path being displayed in the "Delete project"
warning. However, unlike with
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40353, changes in
`Project#to_param` in ea4d6c87 prevented
the wrong project path from being deleted.

While it may have been intentional to retain the failed values, it's
better to be safe and reset all the values back to their persisted
state.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/241110