Don't assign pipeop predict type if it does not change anything

... since PipeOp might be upset about assignments, even if they don't do anything https://github.com/mlr-org/mlr3pipelines/blob/cb8265b72a981fc17689ceb500a7ad97f4d5a53d/R/GraphLearner.R#L369 at the same time, we want a !identical check here https://github.com/mlr-org/mlr3pipelines/blob/cb8265b72a981fc17689ceb500a7ad97f4d5a53d/R/PipeOp.R#L406 (we still want *both* because some 3rd party PO might have read-only active binding