add list semantics to drop grid for accessibility

public/js/components/Drop/Grid.js

@@ -578,9 +578,9 @@ export default {
 		}
 	},
 	template: /* html */`
-	<div
+	<ul
 		ref="container"
-		class="drop-grid position-relative h-0"
+		class="drop-grid position-relative h-0 list-unstyled"
 		:style="gridStyle"
 		@dragover="dragOver"
 		@drop="dragEnd"
@@ -614,5 +614,5 @@ export default {
 				</template>
 			</grid-item>
 		</TransitionGroup>
-	</div>`
+	</ul>`
 }

public/js/components/Drop/Grid/Item.js

@@ -20,7 +20,7 @@ export default {
 		
 	},
 	template: /* html */`
-	<div class="drop-grid-item" @dragstart="tryDragStart">
+	<li class="drop-grid-item" @dragstart="tryDragStart">
 		<slot v-bind="item"></slot>
-	</div>`
+	</li>`
 }