Add missing static to secp256k1_schnorrsig_sign_internal
Add missing static to secp256k1_schnorrsig_sign_internal

ElementsProject/secp256k1-zkp,bitcoin/secp256k1,bitcoin/secp256k1,bitcoin-core/secp256k1,bitcoin/secp256k1,peterdettman/secp256k1,bitcoin-core/secp256k1,bitcoin/secp256k1,peterdettman/secp256k1,bitcoin/secp256k1,ElementsProject/secp256k1-zkp