Neck biting is a natural instinct for cats and is absolutely fine in the right context. Gentle biting to communicate their needs is to be expected. Biting as part of play behavior or as a way to show they are feeling overstimulated is an essential part of your cat's communication kit.
Playtime is a wonderful opportunity for your cat to express themselves. Aggressive biting is less desirable, however, and can cause injury to other cats. In these circumstances, it is crucial to determine any triggers and address these first.