function Drupal\Node\NodeForm::save() does not return a value

This issue is being reviewed by the kind folks in Slack, #needs-review-queue-initiative. We are working to keep the size of Needs Review queue [2700+ issues] to around 400 (1 month or less), following Review a patch or merge request → as a guide.

This will need a test case showing the issue.

This can't be tested because that return type is bogus. save() is used as a submit callback, submit callbacks have no return value. This was just copied from the Entity save method for no reason. We should instead remove the @return from \Drupal\Core\Entity\EntityFormInterface::save().