The tag alias #76910 multi-limbs -> multi_limb is pending approval.

Reason: Adds the alias multi-limbs to multi_limb.

The underscore version multi_limbs is already present, and multi_arm and multi_breast already have the respective aliases in the same format of multi-arms and multi-breasts.

multi-limbs has been mistagged before in practice: https://e621.net/post_versions?commit=Search&search%5Btags_added%5D=multi-limbs