f error if 2 witness elements for P2TR spend

Author: dunxen

lightning/src/ln/channel.rs

@@ -7694,6 +7694,14 @@ where
 							),
 						});
 					}
+					// Bitcoin Core will not relay transactions with a taproot annex yet.
+					if witness.len() == 2 {
+						return Err(APIError::APIMisuseError {
+							err: format!(
+								"The witness for input at index {input_idx} for a P2TR spend has 2 elements (probably includes an annex). The transaction won't be relayed",
+							),
+						});
+					}
 					let sighash = cache
 						.taproot_key_spend_signature_hash(
 							input_idx,