Fix ItemSlots prediction (#25552)

IDK what this arg is for but seems okay with guns. Without it it always thinks the insertion can work.

(cherry picked from commit ad29dbe302ac921b9e3f6cbd3ded79788db27b46)

Content.Shared/Containers/ItemSlot/ItemSlotsSystem.cs

@@ -274,7 +274,7 @@ namespace Content.Shared.Containers.ItemSlots
             if (ev.Cancelled)
                 return false;
 
-            return _containers.CanInsert(usedUid, slot.ContainerSlot, assumeEmpty: true);
+            return _containers.CanInsert(usedUid, slot.ContainerSlot);
         }
 
         /// <summary>