Fix spec failures

We want the `new_item` to be a new, unplaced item.

We have made `move_sequence` a private method, so we need to call it
using send.

ee/spec/models/concerns/epic_tree_sorting_spec.rb

@@ -108,7 +108,7 @@ RSpec.describe EpicTreeSorting do
 
     def move_sequence(range)
       dx = 500
-      RelativePositioning.mover.context(item).move_sequence(range.first, range.last, dx)
+      RelativePositioning.mover.context(item).send(:move_sequence, range.first, range.last, dx)
     end
 
     context 'when self is an epic' do

spec/support/shared_examples/models/relative_positioning_shared_examples.rb

@@ -17,7 +17,7 @@
 RSpec.shared_examples 'a class that supports relative positioning' do
   let(:item1) { create_item }
   let(:item2) { create_item }
-  let(:new_item) { create_item }
+  let(:new_item) { create_item(relative_position: nil) }
 
   let(:set_size) { RelativePositioning.mover.context(item1).scoped_items.count }