rpcwallet: don't re-use sign desc in loop

This commit fixes an issue with signing for mixed inputs in a remote
signing setup where the re-use of the sign descriptor would lead to the
sign method not being reset correctly if a p2wkh input is following a
p2tr input.

lnwallet/rpcwallet/rpcwallet.go

@@ -139,12 +139,15 @@ func (r *RPCKeyRing) SendOutputs(outputs []*wire.TxOut,
 	// We know at this point that we only have inputs from our own wallet.
 	// So we can just compute the input script using the remote signer.
 	outputFetcher := lnwallet.NewWalletPrevOutputFetcher(r.WalletController)
-	signDesc := input.SignDescriptor{
-		HashType:          txscript.SigHashAll,
-		SigHashes:         txscript.NewTxSigHashes(tx, outputFetcher),
-		PrevOutputFetcher: outputFetcher,
-	}
 	for i, txIn := range tx.TxIn {
+		signDesc := input.SignDescriptor{
+			HashType: txscript.SigHashAll,
+			SigHashes: txscript.NewTxSigHashes(
+				tx, outputFetcher,
+			),
+			PrevOutputFetcher: outputFetcher,
+		}
+
 		// We can only sign this input if it's ours, so we'll ask the
 		// watch-only wallet if it can map this outpoint into a coin we
 		// own. If not, then we can't continue because our wallet state