Drag is translating `margin-top` upward on other sortable-items

**Describe the bug**
I have a draggable list that for the most part is uniform, but some of the sortable-items have different content and have margin-top in them to match the screen designs. When I begin to drag any item without margin-top, any sortable-item that does have margin-top is translated upward by the margin-top value.

**To Reproduce**
Create any sortable-list with an item that has margin-top in it (from my testing it doesn't matter if the style is right on the sortable-item or even on a child DIV inside the sortable-item). Begin dragging an item that does not have margin top. As soon as the drag starts, the rows with margin-top are translated upwards. You can see this if you look in the element inspector, as those rows have a `transform: translateY()` style applied to them.

Also can be reproduced by going to the [demo page](https://adopted-ember-addons.github.io/ember-sortable/demo/) and adding margin-top to any row in the first draggable, then dragging any of the other rows (so for example, adding margin to "Dos" and starting to drag "Uno").

**Expected behavior**
Starting a drag should not cause other items in the list to jump position.

Reproduce on the linked demo page by adding margin-top to a row such as "Dos" and dragging another row such as "Uno". Then inspect where ember-sortable computes and applies translateY() during drag. Done means items with margin-top no longer jump upward when a different item starts dragging.

Rédigé par le modèle d'indexation à partir du texte de l'issue.