It seems that having the checkbox in the PR template and failing the action is confusing and not very clear. Let's remove it completely and just add to the template an explanation to explain the backport reason
Closesscylladb/scylladb#18708
Today with the backport automation, the developer added the relevant backport label, but without any explanation of why
Adding the PR template with a placeholder for the developer to add his decision about backport yes or no
The placeholder is marked as a task, so once the explanation is added, the task must be checked as completed